Another awesome Korean drama! This one's called Sungkyunkwan Scandal ~
Here's a short summary from Dramawiki
Sungkyunkwan Scandal is set in Sungkyunkwan University in the late Joseon era during the reign of King Jeongjo, revolving around the exploits and love stories of four youths. When her younger brother's illness worsens and their family is in danger of being evicted from their house for lack of money, Kim Yoon Hee enters the school under his name, disguised as a boy in her desperation to support him. There, she becomes friends with the intelligent and upright Lee Sun Joon, the playboy Goo Yong Ha and rebellious Moon Jae Shin.
I don't normally watch historical dramas, but this one is written in a very "modern" way, so there was a lot of comedy in it. The drama just never ends and each solved cliff hanger led right to another xD There were so many unexpected twists that I never expected would happen, which makes the drama all the more interesting.
Overall, a highly recommended drama! Very cute and entertaining =)