This study examines the climatological variability of urban area and the increase of temperature by urbanization using the observed data of Busan and Mokpo during the last 100 years (1910~2010). The results are as follows. First, the maximum temperature in Busan during the last 100 years has increased by $1.5^{circ}C$ while average temperature and the minimum temperature have increased by $1.6^{circ}C$ and $2^{circ}C$. In Mokpo, the maximum temperature and average temperature have increased by $1^{circ}C$ and the minimum temperature has increased by $0.8^{circ}C$. The increase of urban temperature appeared to be higher in Busan than in Mokpo by $0.5^{circ}C{sim}1.2^{circ}C$. Second, as for the change in temperature before and after urbanization, the maximum temperature, average temperature and the minimum temperature during last 50 years compared to the previous 50 years have increased about $1.5^{circ}C$, $1.6^{circ}C$ and $2.1^{circ}C$, however, the predicted temperature after removing urbanization effect was estimated to be increased by $1^{circ}C$. The proportion that urbanization takes on the overall increase of temperature appeared to be 33% at the maximum temperature, 37.5% at average temperature and 52.3% at the minimum temperature, thus the proportion of urbanization appeared to be maximized at the minimum temperature.