Heat stress is a serious problem among agricultural workers. Workers who are exposed to the extreme heat or work in hot environments may be at risk of heat stress. The physiological changes and heat related symptoms could occur due to heat stress. The objective of this cross-sectional study was to determine the impact of heat on the health and productivity of cassava farm workers in Kratie province of Cambodia. The sampling method was a convenient sampling with some inclu- sive criteria. A total of 125 cassava farm workers were selected to participate in this study. The information was collected through a face to face interview using a questionnaire form. Questions were asked on heat exposure during work and heat related symptoms. The environmental heat was measured using heat stress monitor WBGT and data logger for 2 hours for each day. Automatic blood pressure monitor was used to measure blood pressure and heart rate, while ear thermometer measured the body temperature. All measurements of physiological changes were conducted during the rest and work time of the workers. Observations were conducted to determine the production hourly output of workers by using productivity forms. The productivity was determined by calculating the total of cassava roots harvested per hour, which started from
9.00 a.m. to 11.00 a.m. The results indicated that the highest average of heat stress index were 32.11°C and 32.36°C re- spectively whereby the daily exposure to heat during work, exceeded the threshold limit value (TLV) of 27.5°C for heavy metabolic workload level with 75% work, 25% rest regimen. Meanwhile, the highest prevalence of heat related symptoms reported among workers were tiredness/weakness (84.4%), followed by heavy sweating (82.4%) and headache (61.6%). The blood pressure, heart rate and core body temperature were below the standard, indicated that the workers were fully acclimatized. There was no significant difference in the physiological changes between male and female during the resting and working period. Heavy sweating, heat, BMI and working time were the factors that were significantly related with productivity. In conclusion, the cassava farm workers in Kratie, Cambodia were exposed to high level of heat stress, which reduced their work productivity.