Kyunggi High School (Korean: 경기고등학교; Hanja: 京畿高等學校) is the oldest modern high school in Korea, located in Gangnam District, Seoul. The school is an all-boys school, and its counterpart is Kyunggi Girls' High School [ko], also located in Gangnam District, Seoul.

Kyunggi High School has educated many leaders of the South Korean society. It is the "K" in the so-called "K-S mark," an informal reference to educational credentials said to ensure career success, with the "S" standing for Seoul National University. Before the abolition of the high-school entrance exams in 1974, it was the highest-ranked school in the country.

The school was established by an edict of Emperor Gojong on April 4, 1899, and opened its doors on November 10, 1900. The school's original name was Gwallib Middle School (관립중학교). Its establishment was part of a general program of educational modernization. This effort at modernization was swallowed up by the Japanese annexation in 1910, but the school itself survived. Originally chartered as a middle school, it became a high school in 1906, though it continued to offer middle-school classes until 1971.

In 2000, the South Korean government issued a commemorative 170-won stamp, marking the school's 100th anniversary.