The effects of different stocking densities on the growth and survival rate of the 3-year-old pacific abalone, Haliotis discus hannai were investigated in marine net cage for a year. Stocking densities in net cage (2.4 × 1.2 m) was set 15, 30, 45 and 60 percentage (= per)/sq m (square meter, m2) with share to cross-sectional area per shelter. The water temperature during the testing period was 8.2℃-22.1℃, and salinity is 33.5 ± 0.6 psu, and dissolved oxygen is 7.87 ± 0.86 mg/L. In the shell length (initial size : 71.50 ± 2.28 mm) growth and shell breadth (initial size : 46.43 ± 2.28 mm) of the test abalones, the absolute growth rate (ARG), daily growth rate (DGR) and specific growth rates (SGR) of the 15 per/sq m and 30 per/sq m were higher than those of 45 per/sq m and 60 per/sq m density group (P < 0.05). Also in the weight (initial weight : 35.7 ± 8.1 g), it showed the same results. In survival rates, it were that 15 per/sq m and 30 per/sq m is significantly higher than 45 per/sq m and 60 per/sq m. Therefore, it was that the 15 per/sq m is optimized stocking density in marine net cages about the 3-year-old pacific abalone over 70 mm size. The result shown that total cross-sectional area under the shelter is based on 15 per/sq m (2.4 × 2.4 m, 354 number in a net cage) is suitable for fast growth and survival. But if the economy consider, optimized stocking density would be appropriate to accept 30 per/sq m (2.4 × 2.4 m, 710 number in a net cage).