Based on the 362 samples of Octopus ocellatus collected during August to October of 2015 in the continental shelf of northern South China Sea,the biological characteristics were studied.The result indicated that the mantle length (ML) ranged from 24 mm to 67 mm, with an average of 43.2 mm, with a high concentration of 35 mm to 50 mm, accounting for about 70.9% of all the samples, and the body weight (BW) ranged from 9 g to 124 g, with an average of 37.0 g, and with a dominative weight from 13 g to 52 g, accounting for about 83.8%, respectively. The composition of ML and BW was different among different waters, and the samples in the Beibu Gulf waters smaller than those in the north of South China Sea. The relationship between the ML to BW was best described by the power function by the Akaike's information criterion (AIC), respectively. The ratio of females to males was 0.66:1. However, individual in the north of South China Sea waters is given priority to with maturity stage, accounted for 66.44%, while in Beibu gulf waters, almost all in the immaturity stage. The feeding stage was mainly in 0 and 1 grades, accounting for 91.4% of all the samples and the food was mainly composed of crustacean.