The objectives of the present study were reviewed to assess the optimal dilution rate, pH and osmolality for sperm motility in rabbit fish (Siganus guttatus Bloch, 1787). Semen were diluted with artificial seawater at ratios of 1:50, 1: 1 00, 1: 150 and 1:200 to find the best dilution ratio for sperm motility. And then, this best dilution rate was used for observing on pH (6, 7, 8, 9) and osmolality (200, 300, 400, 500 mosmol/kg) to find the best pH and osmolality for sperm motility. All observations were replicated three times. The results indicated that the best performance of sperm were shown in the dilution rate 1:50, pH = 8 and osmolality 400 mOsm/kg artificial seawater.