The tidal current observation was carried out to investigate the characteristics of the circulation and diffusion in the vicinity of Kunsan harbor on March 1415, April 1∼2, and 13∼14, 1988. By harmonic analysis, the semidiurnal tidal current of more the amplitude of vibration was prevailed and its rotary direction was anti-clockwise in this harbor. Apparently constant current which is generated by out flow of Geum river was found to flow from Kunsan inner harbor to Janghang with the speed of about 30㎝/sec. It can be easily considered that deposition of much sand and mud which come from Geum river in Kunsan inner harbor and erosion in Janghang harbor will be occurred respectively. Autocorrelation and diffusion coefficient of each components was calculated to study the some characteristics of diffusion. Correlogram of the east-west component current was regular and nearly the same period as semidiurnal current. But it appeared irregular and considerably small value in the north-south component correlogram. Diffusion coefficient was 4 order in X-axis and 2∼3 order in Y axis in each study station.