From 1770, King Yong‐Jo of the Korean Dynasty started to observe precipition by means of the rain gauge, which was first created by King Sae‐Jong in 1440. Those observations were continued until the end of the dynasty in 1914. From 1915 to the present time, observations have been continued using modern instruments and methodology. There are now precipitation records for 218 years. In this article the long‐term fluctuation in the annual precipitation records of Seoul is analysed, and a long‐term plan for water resources development is proposed.