Last name 小口 (小口 
) , in the world, is a very rare cognomen. The surname 小口 is habitual in Eastern Asia, particularly China, where it is an extremely rare surname. More prevalently, 小口 is the forename as well as the last name.
| VARIANT | COUNTRY |
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| 小口 | China |
| 小口太郎 JP (b. 1897) |
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| 小口忠彦 Japanese psychologist, JP (b. 1917) |
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| 小口雅之 Japanese boxer, JP (b. 1977) |
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| 小口桃子 Japanese photo model, JP (b. 1987) |
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| 小口ひとみ Japanese actor and announcer, JP (b. 1988) |
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