TOKYO, Feb 12 (Reuters) - Oasis Management, a Hong Kong-based activist fund, said it is opposed to Taisho Pharmaceutical's $5 billion management buyout as it believes the acquisition price was too low.

The Japanese firm's founding family gained 73% of the company in a tender offer last month for 8,620 yen per share - in the country's largest management buyout to date. That represented a 55% premium to Taisho's share price before the offer was announced but was still below book value.

The family is seeking support for a reverse stock split in March that would consolidate Taisho's shares - a vote it is sure to win as it commands more than the two-thirds of vote needed to secure approval.

But under a so-called appraisal process, shareholders could go to court to seek a higher price. The process is designed to protect investors who oppose a buyout by allowing them to ask a judge to determine the fair value of a stock.

"We think the company should be taken away...at least (for) 11,000 yen (per share)," Seth Fischer, Oasis's founder and chief investment officer, told an investor event organised by Monex Group.

Fischer said the stock had long underperformed prior to the buyout, adding that Oasis has been a Taisho shareholder "for a long period of time."

He did not disclose the size of Oasis's stake or elaborate on what steps Oasis might take.

(Reporting by Makiko Yamazaki; Editing by Edwina Gibbs)