PNG file from PS with Transparent Bg turns White when Imported to Unity

After editing some stuffs @ Photoshop CS4, and having my png files ready to be imported, suddenly after importing the png files background turns white… what should I do to maintain the transparency of my png images??

RSVP

http://www.google.com/url?sa=t&rct=j&q=jessyuv+transparent&source=web&cd=3&ved=0CDkQFjAC&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DsMR_R72bWzw&ei=P6TXTpCfC4nu2gXhpPHLDg&usg=AFQjCNEhR7TFoTdUQ3579SiW47YuT5Qp7A