he aims of this study were to apply the Geo-information technology for coastal vulnerability assessment of Phetchaburi coast, which depended on seasonal changed (by influence of Southwest monsoon and Northeast monsoon). The assessment uses a coastal vulnerability index (CVI), consists of a physical environment vulnerability index (PVI) and the socio-economic vulnerability index (SVI) with 9 variables; coastal slope, mean tidal ranges, average wave height, rates of coastal erosion, population density, land use, built-up, transportation and coastal protection measures. The results showed, the different during monsoon had an indecisive difference effect on mean tidal ranges, average wave height, and changes in the coastline. However, the monsoon had effected to sand sediment of the beach.