The aims of this research were to investigate the effects of soil moisture on cassava growth and physiological processes and to determine the critical soil moisture contents. To fulifll the research objectives, cassava was grown under five levels of soil moisture, including 50, 40, 30 and 20% of soil available water holding capacity (AWHC) along with control (no irrigation). Physiological traits and plant growth parameters were measured. The results showed that cassava grown under 50% of AWHC exhibited the highest photosynthesis rate, stomatal conductance, predawn leaf water potential and chlorophyll activity. All physiological traits decreased significantly when the moisture content was less than 40 and 20% of AWHC in sandy clay loam and loamy sand soil, respectively. Predawn leaf water potential was used to determine the critical point of soil moisture. It was found that the critical soil moisture contents were 39.0 and 15.7% of AWHC in sandy clay loam and loamy sand soil, respectively.