To investigate whether the rearing environmental factors (size heterogeneity, rearing density, and feeding frequency) affect the growth and cannibalism of fry in cultured puffer Takifugu obscurus, we conducted three experiments. To examine size effects, we used small (total length [TL] $26.0{pm}0.5;mm$, body weight [BW] $0.18{pm}0.01;g$), medium (TL $23.1{pm}0.1;mm$, BW $0.28{pm}0.01;g$), large (TL $26.0{pm}0.2;mm$, BW $0.48{pm}0.01;g$) and small-large size combination groups. For density, we used size-matched puffers (TL $25.0{pm}0.5;mm$, BW $0.53{pm}0.03;g$) and five density were examined ranging from 1.43 to 7.14 individuals/L. For the feeding frequency, we also used size-matched fry and feeding frequencies of three times/2 days, one time/day, two times/day, three times/day. We ran each experiment in triplicate and investigated the survival rate, daily food intake (DFI), feed efficiency (FE), and daily growth rate (DGR). The growth of the puffers increased with increasing size, density, and feeding frequency, while cannibalism increased with a greater size gap, density and lower feeding frequency. Therefore, we concluded that size, rearing density, and feeding frequency are major factors influencing growth and cannibalism of the puffer, T. obscurus.