Post a character that looks like a girl, but is actually a boy.

Ryuunosuke from Sakurasou no Pet na Kanojo

Kuranosuke from Kuragehime

Ritsu Sohma- Fruits Basket

China/Yao Wang(Hetalia)

Grell xD

Yuri Kamanosuke Храбрая сердцем 10 (Male)

i'm restraining myself to say that grell is a trans girl meaning she actually is female on the post,,

Anyway, here, Chihiro:

Haku (Naruto)

Reiji Uno and Eiji Saga from Cardfight!! Vanguard. Eiji (brown hair) I thought was just a tomboy, but Reiji... I got nothin'. He looks and sounds like a 10 год old girl.

Ayame from Fruits Basket
And Haruhi's dad from Ouran

Saika Totsuka from My teen romantic comedy Snafu

Kurama/Shuichi Minamino from YYH~ I Любовь this guy!

Aoi Hyoudou from Kaichou wa Maid Sama!
I was thoroughly convinced Aoi was a girl until the end of that episode . . .

Haku~Naruto

He! Nagihiko Fujisaki from Shugo Chara. Everyone thought he's a girl çuz he appears at Episode 2 with a red cape (red capes at Guardians means a girl) and he's also at the Q- Chair ( Queen Chair ). But for me, Nagihiko is a boy, LOL. PLUS- His name when he is a boy, Nagihiko but when he was introducing as a girl (with a cute voice) he's Nadeshiko. Oh god, he have two guardians too, Rhythm is a boy, and Temari is a girl. Heh heh, he character transformed in both of them.

Ciel Phantomhive of Black Butler

Ciel Phantomhive looks like a girl when dressed as such.

Sasaki Yuuta from Cuticle Detective Inaba comes to mind for me here.

KAWAII!!

Alluka Zoldyck,at first I thought he was a girl but then the wiki сказал(-а) Alluka was a boy

Poland from Hetalia

Envy from Fullmetal Alchemist