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Objective: To investigate the maturity development of miracidia in uterine eggs from four portions of the Opisthorchis viverrini uterus and environmental factors possibly affected in maturation and infectivity of distal part uterine eggs. Methods: Uteri of adult worms were divided into 4 equal parts. Development of eggs was determined under light microscope. Only embryonated eggs were used to evaluate the effects of physicochemical factors: temperature, salinity, acidity, ultraviolet A, B, C. Infection success was evaluated by feeding treated eggs to intermediate host snails and determining by using a PCR approach. Results: Eggs obtained from the uterus closest to the ovary (regions 1 and 2) failed to develop in vitro. Eggs from region 4 of the uterus (close to the genital pore) were used to study effects of physicochemical factors. The highest survival and infection success was in groups of eggs kept at 30 ℃ (95.20％). The calculated period of loss infection success (LI50 and LI95) on miracidia in distal uterine eggs by exposure to UV-A, UV-B and UV-C were 73 and 1523 d; 8 and 20 d; 1 and 2 d, respectively. Lethal concentrations (LC50 and LC95) of salinity, HCl and NaOH on miracidia in distal uterine eggs were 45.43 and 120.09 ppt, 0.01 and 0.25 M; 0.01 and 0.11 M, respectively, after 24 h exposure. Conclusions: Opisthorchis viverrini eggs display a high tolerance to environmental conditions, especially after snail host eating for infection.