Tropical countries are facing a rapid change in land use/land cover with increasing water demand for agriculture and industry. Hydrological issues thus become more and more important in these regions than ever before. The root zone soil moisture content (SMC) derived from our proposed retrieval algorithm in conjunction with the apparent thermal inertia approach and Moderate Resolution Imaging Spectroradiometer (MODIS) imagery from 2004 to 2008 over the tropical catchment in northern Thailand was presented in this study. The results showed that the Pearson correlation coefficient and Nash-Sutcliffe efficiency coefficient between ground truth and retrieved SMC under all different land cover sites varied respective 0.81-0.88 and 0.44-0.67. The retrieved precision referred to Root Mean Square Error value varied between 0.012 and 0.058 (m 3. m-3). The successful root zone SMC estimation by using MODIS data will contribute to water management of the tropical or subtropical hydrological studies in the future.