What's the Sailor Moon theme song? I remember watching the series when I was little, but I completely forgot the song!

It's "Moonlight Densetsu" :
link
I 爱情 this song :D

In 1, 2, 3, 4 seasons theme song is Moonlight Densestu (Moonlight Legend).
5's season theme song is Sailor 星, 星级 Song.

in English it's a theme song for children, in Japanese it's actually about romance called Moonlight Desetsu

the last part meanig legend