To explore the relationship between morphological phenotypes, internal organ size and immune function and specific life history phases before and after metamorphosis in rice frogs, Fejervarya multistriata, tadpoles at different developmental stages from Gosner 37-stage to Gosner 46-stage were sampled, and the variations of body size, internal organ index and the responsiveness to phytohemagglutinin (PHA-P) for multiple key life history phases were measured, respectively. The results were as follows: (1) The body mass, body width, tail length, and total body length was gradually increased from Gosner stage 37 to 40-41 tadpoles, and then declined with a minimum at Gosner stage 46 froglets (P < 0.05). The snout to vent length showed the highest value at Gosner stage 42-43 tadpoles, which was significantly higher than that of Gosner stage 37 tadpoles and Gosner stage 46 froglets (P < 0.05). (2) The wet mass index of livers, fat bodies and kidneys peaked at Gosner stage 44-45 tadpoles, all showed the minimum value at Gosner stage 38-39 tadpoles (P < 0.05); The wet mass index of gill or lungs peaked at Gosner stage 37 tadpoles, which was significantly higher than that of any other developmental stage (P < 0.05); The length index of digestive tract was greatly higher at Gosner stage 37, 38-39 and 40-41 tadpoles than that of Gosner stage 42-43 and 44-45 tadpoles and Gosner stage 46 froglets (P < 0.05). No significant developmental stage differences were found for the wet mass index of heart and spleen (P > 0.05). (3) The maximal value for the PHA-P response of Gosner stage 37, 38-39 and 42-43 tadpoles appeared 2 h, 3 h, and 4 h after