To evaluate the effect of different concentrations of reduced glutathicne (GSH) supplemented to the freezing extender on motility, livability and abnormality of Friesian bull spermatozoa during cooling, freezing and thawing phases of the cryopreservation process, a total of five Holstein bulls with average age of 3.5 years were used in this investigation. Semen ejaculates were collected twice weekly by means of artificial vagina. Only ejaculates having mass motility of 70% or more was pooled for each collection day for 5 weeks. The pooled semen was divided into 4 parts including control, and three concentrations of GSH (0.4, 0.8 and 1.2 mM). Percentages of motility, livability and abnormality were determined during different following phases of cryopreservation process: initial percentage in pooled semen pre- dilution; post-dilution; post-equilibration period and post-thawing. Results show insignificant effect of GSH concentration on sperm motility post diiution. During equilibrium period, sperm motility was higher (P<0.05) with 0,4 GSH than 0 and 1.2 mM GSH (68.0 vs. 58.5 and 60.0%, respectively), but did not differ Significaniiy than semen with 0.8 mM GSH. However, the differences between semen with 0.8 mM GSH and the other concentrations wer not significant. in frozen-thawed semen, sperm motility was higher (P<0.05) with 0 04 and 0.8 mM GSH than 0 and 1.2 mM GSH (55.5 and 51.0% vs. 33.0 and 381%, respectively). The lowest (P<0.05) reduction in sperm motility during all semen processes was obtained With 0.4 or 0.8 mM GSH, which resulted in the highest recovery rate (74%) of motile spermatozoa in thawed semen. The effect of GSH concentration on live sperm percentage post dilution was not significant. Post 4 h at 4°C as an equilibrium period. live sperm percentage was higher (P<0.05) with 0.4 mM GSH (68.4%) than 0, 0.8 and 1.2 mM GSH (60.7, 63.4 and 62.2%, respectively). Post freezing and thawing, sperm livability in semen diluted with 0.4 and 0.8 mM GSH was higher (P<0.05) than 0 and 1.2 mM GSH (56.8 and 51.3 vs. 35.2 and 40.6%, respectively) The lowest reduction in sperm livability during all semen processes was obtained with 0.4 or 0.8 mM GSl—l, which resulted in the highest recovery rate (71.4%) of live spermatozoa. The effect of GSH concentrations on sperm abnormality, post dilution, during equilibrium period, and post freezing and thawing was not significant. The lowest (P<0.05) increase in sperm abnormality during all semen processes was obtained with 0.4 mM GSH, In conclusion, the addition of GSH with a concentration of 0.4 mM to the freezing Tris—extender improved percentages of motility, livability and abnormality of bull spermatozoa.