Responses of the oriental fruit fly, Bactrocera dorsalis (Hendel), third instar larvae to desiccation and immersion were examined at 25°C in the laboratory condition. Third instar larvae desiccated in dry soils (0% field capacity) did not survive beyond 12 h, nor submerged under water beyond 3.5 d. The time to 50%, 90%, and 99% mortality (LT₅₀, LT₉₀, and LT₉₉) were 5.67, 8.60, and 10.99 h respectively in desiccation condition, and 1.81, 2.49, and 3.06 d in immersion test. The average eclosion time of survived flies was not significantly affected by the desiccation time, while that increased linearly with increasing immersion time. Cumulative weight loss of larvae increased curvilinearly with desiccation time, and the rate of weight loss was greatest during the first 2 h. The relationship between the mortality and the percentage of cumulative weight loss was described by Probit model in desiccation. It was estimated that when the percentage of cumulative weight loss was 29.1%, 36.7%, and 43.0% respectively, the mortality rates was 50%, 90%, and 99% correspondingly.