Oh Ha Ni (Jung So Min) is a sweet lively and happy high school student yet she is definitely not the sharpest crayon in the box.
She has a crush on Baek Seung Jo (Kim Hyun Joong), the smartest boy in school despite being chased loyally by Bong Joon Gu herself. When she confesses to Seung Jo through a letter, he brings it back to her, after grading it harshly and commenting that he hates stupid girls.
When Oh Ha Ni's new house suddenly collapses her father's friend offers for him and Ha Ni to stay with them. Unknown to Ha Ni, her father's friend is actually Baek Seung Jo's dad.
As they continue to live under the same roof and attend Parang University together, Ha Ni continues to show affection for Seung Jo although he seems to be more interested in the equally clever and beautiful Yoon Hae Ra (Lee Si Young).
Playful Kiss is based on the Japanese shōjo manga, Itazura Na Kiss.