The effect of stocking density on growth performance of Thai abalone, Haliotis asinina, Linnaeus 1758, was investigated over an 8-mo period (July 2008 to March 2009). A semiclosed recirculating land-based system was used with stocking densities of 368, 735, and 1,100 individuals/m². Each stocking density had 3 replicates. An artificial diet, modified from a shrimp commercial diet, was used throughout this experiment. In July 2008, initial sizes of abalone (mean shell length (SL) ± SE) were not statistically different, with values of 1.28 ± 0.0062, 1.28 ± 0.0131, and 1.30 ± 0.0339 cm for 368, 735, and 1,100 individuals/m², respectively (P > 0.05). After 8 mo, SLs were significantly different, with values of 3.63 ± 0.092, 3.25 ± 0.1173, and 3.05 ± 0.0985 cm for the 3 stocking densities. As the stocking density increased, mean specific growth rates, measured by the percent increase in SL during the 8-mo period, decreased, with values (mean ± SD) of 1.97 ± 0.0495, 1.66 ± 0.1595, and 1.53 ± 0.0544. The mean specific growth rate of the density 368 individuals/m² was significantly different from 735 individuals/m² and 1,100 individuals/m². The variations of specific growth rate, calculated in term of the coefficient of variation (mean ± SD) were increased with increasing stocking densities: 20.16 ± 0.251, 22.17 ± 3.146, and 23.66 ± 0.886. The difference was significant only between the 368 individuals/ m² and the 1,100 individuals/m². The best-fit linear equations between the natural logarithm of specific growth rate and initial size of abalone for 3 stocking densities were estimated. These equations demonstrated that specific growth rates of the larger size abalone decreased at higher rates than that of the smaller size as the stocking density increased. This demonstrated a nonrandom effect of stocking density on abalone size. This also implied that grading of large abalone should be done regularly. Allometric equations between shell width (SW) and SL as well as between total weight (TW) and SL were calculated: SW = 0.6531 SL^0.777 (r² = 0.721) and TW = 0.3276 SL^2.720 (r² = 0.823), respectively. Throughout this 8-mo experiment, survival rates of abalone were not significantly different, with values of 95.1 ± 5.05, 92.9 ± 6.19, and 95.7 ± 0.513 at stocking densities of 368, 735, and 1,100 individuals/m², respectively.