Main Street Capital Set to Join Russell 3000(R) Index

Indicates Automatic Inclusion in Widely Followed Russell 2000(R) Index

HOUSTON, June 16 /PRNewswire-FirstCall/ -- Main Street Capital Corporation
(Nasdaq: MAIN) ("Main Street") announced today that it is set to join the
broad-market Russell 3000(R) Index when Russell Investments ("Russell")
reconstitutes its comprehensive set of U.S. and global equity indexes on June
26, 2009, according to a preliminary list of additions posted on June 12, 2009
at www.russell.com. Inclusion in the Russell 3000 Index indicates that Main
Street, based upon its total market capitalization, will also automatically be
included in the widely followed Russell 2000(R) Index for U.S. small-cap
stocks.

The annual reconstitution of Russell's U.S. indexes captures the 4,000 largest
U.S. stocks as of the end of May, ranking them by total market capitalization.
Membership in the Russell 3000 Index, which remains in place for one year,
means automatic inclusion in the large-cap Russell 1000(R) Index or small-cap
Russell 2000 Index, as well as the appropriate growth and value style indexes.
Russell determines membership for its equity indexes primarily by objective,
market-capitalization rankings and style attributes. The Russell 3000 Index
also serves as the U.S. component of the Russell Global(R) Index, which
Russell launched in 2007. The Russell indexes are widely used by investment
managers and institutional investors for index funds and as benchmarks for
both passive and active investment strategies. An industry-leading $4 trillion
in assets currently are benchmarked to them.

Total returns data for the Russell 3000 Index and the Russell Global Index, as
well as other Russell Indexes, is available at
www.russell.com/Indexes/performance/default.asp.

ABOUT MAIN STREET CAPITAL CORPORATION
Main Street (www.mainstcapital.com) is a principal investment firm that
provides long-term debt and equity capital to lower middle market companies.
Main Street's investments are made to support management buyouts,
recapitalizations, growth financings and acquisitions of companies that
operate in diverse industry sectors and generally have annual revenues ranging
from $10 million to $100 million. Main Street seeks to partner with
entrepreneurs, business owners and management teams and generally provides
"one stop" financing alternatives to its portfolio companies.

Forward-Looking Statements
This press release may contain forward-looking statements. Words such as
"estimates", "expects", "expected", "believes", and "future" or similar
expressions are intended to identify forward-looking statements. Any such
statements, other than statements of historical fact, may be affected by other
unknowable future events and conditions, including elements of the future that
are not under Main Street's control, or factors that Main Street may not have
considered; accordingly, such statements are not guarantees or assurances of
any aspect of future performance. Actual developments and results may vary
materially from these forward-looking statements. Such statements speak only
as of the time when made, and Main Street undertakes no obligation to update
any such statement now or in the future.

Contacts:
Main Street Capital Corporation
Todd A. Reppert, President and CFO
treppert@mainstcapital.com
713-350-6000

Dennard Rupp Gray and Easterly, LLC
Ken Dennard
ksdennard@drg-e.com / 713-529-6600
Augustine Okwu
gokwu@drg-e.com / 404-532-0086

SOURCE Main Street Capital Corporation

Todd A. Reppert, President and CFO of Main Street Capital Corporation,
+1-713-350-6000, treppert@mainstcapital.com; or Ken Dennard, +1-713-529-6600,
ksdennard@drg-e.com, or Augustine Okwu, +1-404-532-0086, gokwu@drg-e.com, both
of Dennard Rupp Gray and Easterly, LLC, for Main Street Capital Corporation