Eighteen ejaculates were collected from three mature Arabian stallions (about 5 years of age) during breeding season. Semen was extended with Tris-yolk fructose extender immediately after collection and evaluated. Diluted semen (0.1 ml) was added to 0.9 ml of Na-citrate-lactose solution to get a final concentration of (50, 100, 150, 200 and 300 mOsm/Kg^-1) and then incubated at 37˚C for up to 60 minutes. After each incubation time (0, 5, 15, 30 and 60 minutes), the response of the stallion spermatozoa to HOS-test was assessed and  the percentage of sperm motility, percentage of spermatozoa with intact acrosome, percentage of spermatozoa with coiled tails and swollen spermatozoa were estimated. The obtained results revealed that, the percentages of motile spermatozoa and spermatozoa with intact acrosomes were significantly (P<0.05) increased, while the percentages of spermatozoa with coiled tails and swollen spermatozoa were significantly (P<0.05) decreased in the extended spermatozoa with Na-citrate-lactose solution at a level of 300 mOsm/Kg^-1 as compared to 50, 100, 150 and 200 mOsm/ Kg^-1, during the incubation at 37ºC for up to 60 minutes. The prolongation of the time of incubation at 37ºC for up to 60 minutes of the extended spermatozoa decreased significantly (P<0.05) the percentages of motile spermatozoa and spermatozoa with intact acrosomes, while increased significantly (P<0.05) the percentages of spermatozoa with coiled tails and swollen spermatozoa extended with Na-citrate-lactose solution at a level of 300 mOsm/ Kg^-1 compared to 50, 100, 150 and 200 mOsm/ Kg^-1. In conclusion, HOS-t could be recommended for semen evaluation in stallions because it is applicable and inexpensive.