Worldwide, Sadao (Sadao 
, サダオ , Садао 
) is a rare principally male, but very infrequently feminine first name. The first name Sadao is habitual in Japan, where it is a rare boy's name, the United States, where it is a very rare principally masculine, but scarcely girly name, and Brazil, where it is a very rare boy's name. More frequently, Sadao is the last name as well as the forename.
| VARIANT | COUNTRY |
|---|---|
| Sadao | Philippines, Japan, China, Brazil, Thailand |
| サダオ | Japan |
| Садао | Russia |
| sena sadao (b. 1716) |
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| sadao mizokami (b. 1870) |
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| sadao saburi (b. 1879) |
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| sadao koiwai 1893 (b. 1893) |
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| sadao otani (b. 1892) |
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| sadao suzuki botanist (1909-1998) (b. 1909) |
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| sadao kawasaki (b. 1901) |
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| sadao aoyama (b. 1903) |
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| sadao wakizaka Japanese field hockey player (b. 1916) |
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| sadao sugaya botanist (b. 1917) |
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| sadao kumagai (b. 1908) |
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| sadao kikuchi (born 1924) (b. 1924) |
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| sadao fujii (b. 1914) |
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| sadao onoda (b. 1918) |
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| sadao matsubashi (b. 1925) |
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