There is many insurance company in Japan, but there just six of them is listed as the largest insurance company over the world by report from AM Best. AM Best is credit ranting agency that listed companies with measured by total non-banking assets and by net premiums written.

Here the list of Japanese insurance companies with asset over 300 billion USD:

1. Nippon Life Insurance Company

Nippon Life Insurance Company (日本生命保険相互会社, Nihon Seimei Hoken Sōgo-gaisha), also known as Nissay (ニッセイ, Nissei) or Nihon Seimei (日本生命) is the largest Japanese life insurance company by revenue. The company was founded in 1889 as the Nippon Life Assurance Co., Inc. In structure it is a mutual insurance company.

In 2018 Nippon Life have assets 710.9 + net premuim 54.3 billion USD, the revenue itself by General insurance, Life insurance, Health insurance products.

2. Japan Post Insurance

Japan Post Insurance Co., Ltd. (株式会社かんぽ生命保険, Kabushiki-gaisha Kanpo Seimei Hoken), is a Japanese life insurer that was established on October 1, 2007, with the privatization of Japan Post Life Insurance (簡易保険, Kan'i Hoken, lit. "Simple Insurance"). It is part of the Japan Post Holdings group. As of 2011, it was the world's fourth largest insurance company as regards net premiums written behind three European insurers and the largest as regards non-banking assets.

JP Insurance offered Whole life insurance, Endowment insurance, Term insurance, Student insurance, and Longevity support insurance. JP Insurance in 2018 have 666.6 billion USD of non-banking assets.

3. JA Kyosai

The National Mutual Insurance Federation of Agricultural Cooperatives (Japanese: 全国共済農業協同組合連合会), commonly known as "JA Kyosai" (ＪＡ共済) or ZENKYOREN, is Japan's national mutual aid association of agricultural cooperatives, founded based on Japan's Agricultural Cooperative Law. ZENKYOREN was founded in 1951 and provides property, liability and life insurance.

JA Kyosai have 529.2 billion USD non-banking assets and 50.3 billion USD from net premiums written in 2018.

4. Dai-ichi Life

The Dai-ichi Life Insurance Company, Limited (第一生命保険株式会社, Dai-ichi Seimei Hoken Kabushiki-kaisha), or Dai-ichi Life for short, is the third-largest life insurer in Japan by revenue, behind Japan Post Insurance and Nippon Life.

Founded on September 15, 1902, Dai-Ichi was one of the oldest mutual insurance companies in Japan until a motion to demutualise was passed in 2009 and, on April 1, 2010, it listed on the Tokyo Stock Exchange, raising 1.01 trillion yen. As of March 2013, it had the most assets of any listed company in Japan with a total of 33 trillion yen on its stand-alone balance sheet, more than twice the total assets of #2-ranked Tokyo Electric Power Company. In 2018 Dai-ichi Life has raising net premiums written 48.2 billion USD and 504.6 billion USD from non-banking assets.

5. Meiji Yasuda Life

Meiji Yasuda Life Insurance Company (明治安田生命保険相互会社, Meiji Yasuda Seimei Hoken Sōgo Kaisha) is a Japanese life insurance company, headquartered in Tokyo and created in 2004 from the merger of Meiji Life and Yasuda Life. The company is one of the oldest and largest insurers in Japan. The Meiji Yasuda Life Insurance Company is a member of the Mitsubishi UFJ Financial Group (MUFJ) keiretsu.

In 2018, Meiji Yada Life assets raising to 379.9 billion USD.