LONDON (Reuters) - Woodford Investment Management sold out of French pharmaceutical firm Sanofi (>> Sanofi) in May on valuation grounds, the money manager said on Thursday, and instead added several smaller firms to its main fund.

Run by star UK fund manager Neil Woodford, the 6.2 billion pounds ($9.6 billion) mutual fund, is a favourite of both retail and institutional investors given his successful long-term track record at his previous firm Invesco.

"This (Sanofi) is still an attractive business operating in a fundamentally undervalued industry, but it is simply a casualty of the competition for capital in the portfolio," the firm said in a blog post.

Woodford also said it had sold off its position in gas-to-liquid fuel technology company Velocys (>> Velocys PLC) given concerns about growing competition.

"Our conviction in the company’s ability to fulfil its potential has diminished, as we now fear that other technologies may overtake it," it said.

The fund added biotechnology firm Horizon Discovery Group (>> Horizon Discovery Group PLC), Norway-based tech company Idex (>> Idex ASA), drug discovery firm Verseon (>> Verseon Corp) and unlisted AJ Bell to the portfolio during the month.

(Reporting by Nishant Kumar; editing by Simon Jessop)