This Study was conducted to determine the effect of diluent supplementation with different levels of garlic extract (GE) on semen quality of cocks during in vitro storage for different periods (24, 48 or 72 hrs).  A total of 42 White Leghorn roosters, 22 weeks old were randomly divided into 6 experimental pens of 7 roosters each . The experimental groups were as follows : T1 = fresh , undiluted semen ( control ) ; T2 = semen diluted 1 : 1 with Lake diluent ( LD ) alone ; T3 = semen diluted 1 : 1 with GE alone, while T4 , T5 and T6 represented semen samples diluted 1 : 1 with LD and supplemented with 1 , 2 and 4 ml GE / 100 ml of diluent , respectively . Semen quality traits involved in this study were mass and individual motility of spermatozoa and percentages of dead and abnormal spermatozoa and acrosomal abnormalities. Results denoted that semen incubation for 24 , 48 or 72 hrs at the refrigerator temperature in the absence of GE ( T1 ) was associated with a significant ( p < 0.05 ) decrease in the mass activity and individual motility , and significant ( p < 0.05 ) increase in the percentages of dead spermatozoa , abnormal spermatozoa and acrosomal abnormalities . However , the inclusion of GE into the LD ( T4 , T5 and T6 ) significantly ( p < 0.05 ) improved motility , viability and normality of spermatozoa acrosomes compared with control group ( T1 ) . Besides , T5 and T6 surpasses all other treatments in ameliorate the deterioration that found in the semen traits included in this study after in vitro storage for up to 72 hrs . In addition, T2 was superior to T3 as regards mass activity and individual motility, whereas there were no significant differences between these two treatments with relation to percentages of live spermatozoa and normal spermatozoa and acrosomes for semen samples stored for 24, 48 or 72 hrs. In conclusion, supplementation of GE into avian semen diluents particularly at the doses of 2 and 4 ml GE / 100 ml of diluent can be used as a successful technique for depresses the detrimental effects of lipid peroxidation which could lead to sperms deterioration during in vitro storage for up to 72 hrs.