(In 13th paragraph corrects website traffic figure to 100 million from 1 million after correction from company)
* No decision yet on possible stock market listing
* Investor Kinnevik figures value business at $5 bln
* Sales growth slows in second half as weather forces discounting
* Breaks even in core German, Austrian, Swiss markets
By Emma Thomasson
BERLIN, Feb 14 Sales growth at Europe's biggest online fashion retailer Zalando slowed in the second half of 2013 ahead of a possible stock market listing as a mild winter led to high levels of discounting.
The Berlin-based retailer, which started selling shoes in Germany five years ago and now ships 1,500 different brands to 15 countries, is seen as a prime candidate to list this year.
Rubin Ritter, member of the Zalando management board, told Reuters that an initial public offering - which could be western Europe's biggest technology offering since German internet service provider T-Online listed in 2000 - was a possibility but not an immediate priority.
"An IPO could be an interesting option going forward but right now there is no decision on this topic," he said.
Shares in Zalando's biggest investor, Swedish firm Kinnevik , which have almost doubled in the last year due to its investments in fast-growing e-commerce, were down 6.5 percent after the Zalando figures.
Kinnevik said on Friday it valued its 36 percent stake in Zalando at 12.14 billion Swedish crowns ($1.9 billion), suggesting the whole company is worth more than $5 billion.
Sales rose 52 percent to 1.76 billion euros ($2.4 billion) in 2013, with the seven new markets it entered in summer 2012 helping drive first-half growth of over 70 percent. That slowed to 42 percent in the third quarter and 36 percent in the fourth.
Last month, shares in Zalando's British rival ASOS, which have jumped 144 percent in a year, slipped after it said retail sales growth slowed to 38 percent in the four months to Dec. 31, compared with 47 percent in the fourth quarter of its 2012-13 year.
Market research firm Mintel estimates online sales made up about 9.9 percent of Europe's clothing and footwear spending in 2013 or about 38 billion euros, up from 8.6 percent in 2012.
"We expect growth in online sales of clothing and footwear to outperform the overall e-commerce market in 2014," said Mintel retail analyst John Mercer.
However, pure online retailers like ASOS and Zalando are facing increasing competition as established brands like H&M and Inditex expand their e-commerce offering.
MOST-VISITED FASHION WEBSITE OUTSIDE CHINA
Data last month showed Zalando saw a sharp slowing in the growth of visitors to its website in December, but Ritter said that did not fully reflect booming use of mobile devices, which now account for over 35 percent of Zalando website visits.
"Our traffic is still growing quite considerably so we have 100 million visits per month which makes us the most visited fashion website outside China," he said.
Zalando said it was breaking even in its core markets of Germany, Austria and Switzerland, where it made more than 1 billion euros of sales in 2013.
Its operating margin improved by 0.5 percentage points from minus 7.2 percent in 2012, but Ritter said that was less than hoped due to the late start of the summer and a mild winter that forced fashion retailers to discount seasonal styles.
Ritter declined to say when the business might turn a profit but said Zalando, which has advertised heavily to win market share, would spend less on marketing as a percentage of sales and keep expanding higher-margin private label brands, although it has no immediate plans to move into new countries.
Zalando, which changed its structure in December to one typically used by German listed companies, said Kinnevik chairman Cristina Stenbeck will take over as chair of its supervisory board from Kinnevik Chief Executive Mia Brunell, who is stepping down from the Swedish group.
Also joining the board is Lothar Lanz, chief financial officer of German publisher Axel Springer which is preparing to list its online classified advertising unit.
($1 = 0.6030 British pounds)
($1 = 0.7317 euros) ($1 = 6.4650 Swedish crowns) (Additional reporting by Mia Shanley in Stockholm; Editing by Erica Billingham and David Holmes)