By Noriko Futamura

TOKYO, Aug 31 (Reuters) - U.S. buyout firm Bain Capital has retained Nikko SMBC Securities to handle an initial public offering of online marketing research firm Macromill Inc, people with direct knowledge of the matter told Thomson Reuters DealWatch.

Bain Capital bought 100 percent of Tokyo-based Macromill through an 51.4 billion yen ($500 million) public tender offer in 2014. Macromill in the same year acquired Dutch peer MetrixLab, which operates in 10 countries, to expand its global reach.

The IPO will likely take place next year, said the people, asking not to be identified because the process is private.

A Bain Capital representative declined to comment.

($1 = 103.1800 yen) (Reporting by Noriko Futamura; Writing by Junko Fujita; Editing by Ruth Pitchford)