The South Korean bourse on Thursday approved an estimated $4 billion IPO by leading life insurer Samsung Life Insurance, paving the way for what is likely to be the country's biggest share float in May.

The offering by Samsung Life, which is part of South Korea's top business conglomerate Samsung Group, comes as the market waits for the pricing next week of an up to $12 billion offering by Japan's Dai-ichi Mutual Life Insurance, the world's largest IPO since credit card firm Visa raised $19.7 billion in 2008.

Fund managers and analysts are cautious in predicting demand for Samsung Life, ranked 14th among global life insurers in premiums received, making it bigger than Dai-ichi, but said the IPO would attract developing market-focused funds.

Samsung Life has split its shares at 1-to-10 to help spur trading ahead of the IPO. The stock last traded at 115,000 won ($101.5) in the over-the-counter market for unlisted stocks, according to the Presdaq Web site.

Dai-ichi will price its shares at between 125,000 yen and 155,000 yen ($1,385-$1,717) each.

Which (of Dai-ichi and Samsung Life) would attract more foreign investor community's attention will depend on final pricing of the IPO, because basically their business model is very similar, said one analyst, who declined to be named.

Analysts expect Samsung Life's pricing to be in line with the current over-the-counter market price. The exact size of the offering has yet to be set, although many see it topping 4 trillion won.

Last week, second-ranked Korea Life priced its 1.8 trillion won ($1.6 billion) IPO below its indicative range as fund managers said foreign investors pushed for lower prices ahead of the two larger upcoming deals.

Managers handling developed market funds will probably focus on Dai-ichi, and those who invest more heavily in developing markets will allocate more to Samsung Life, said a senior fund manager at a European fund house who also declined to be named.

At end-2009, Samsung Life was 21 percent-owned by Samsung Group's former chairman Lee Kun-hee. Samsung Everland, a de-facto holding company for the group, holds 19 percent and Shinsegae has 14 percent.

Goldman Sachs and Korea Investment & Securities are leading bookrunners of the Samsung IPO.

($1=1133.4 Won)

(Editing by Jonathan Hopfner and Ian Geoghegan)