TOKYO, April 4 (Reuters) - Hong Kong-based activist investor Oasis Management said on Thursday it would start a campaign against Kao Corp, demanding that the Japanese cosmetics and skincare firm redefine its brand portfolio and improve marketing.

"If Kao focused on its cosmetics and health & beauty segments and improved marketing, Oasis believes its stock price would exceed 10,000 yen per share, a 76% upside from current levels," the hedge fund investor said in a statement.

Oasis said Kao should prioritize the international growth of its core cosmetics and skincare brands, and hire a chief marketing officer or equivalent with global experience to transform its marketing strategy.

Kao has a product portfolio that can compete directly with Beiersdorf, L'Oreal, Estee Lauder and Procter & Gamble, and turn it into a global leader, the activist investor said.

Oasis did not say how much stock it owns in Kao.

Kao could not be reached for immediate comment. (Reporting by Makiko Yamazaki; Editing by Sandra Maler and Tom Hogue)