Rice is the most important staple food in Thailand, and an economically important export crop. Thailand is one of the largest rice producers and exporters in the world. In Thailand, rice planting season is also the rainy season, and cloudy weather is therefore very common. In recent years, Synthetic Aperture Radar (SAR) imagery is playing a more important role in rice crop mapping because of its advantage of using microwave that can penetrate clouds. The aim of this study is to map the rice area in Ayutthaya province, Thailand using Sentinel-1 SAR images during the wet-season (May-August) in 2015. The Ayutthaya province, located in the central area of Thailand, is one of the important rice production areas in the country. Three essential steps are required to conduct the study: (1) image pre-processing, including radiometric correction, geometric correction, and speckle noise removal; (2) rice area mapping, including Normalized Difference Sigma-0 Index (NDSI) calculation and NDSI thresholding; and (3) assessing mapping accuracy, by comparing with ground truth data. This study shows the applicability of Sentinel-1 SAR imagery for rice crop mapping during the cloudy wet-season in Thailand.