Good semen quality plays a very important role in promoting poultry breeding programs; due to its antioxi-dant properties and role in fat metabolism, L-carnitine seems to be effective in improving semen quality. Therefore, this study was performed to evaluate the effect of dietary L-carnitine supplementation on the motility parameters and qualitative traits in semen Cobb breed roosters. A total of twenty roosters, 24 weeks-old Cobb roosters randomly assigned to four experimental groups. The experimental design was conducted in a completely randomized design with 4 experimental treatments (T1: 0, T2: 125, T3: 250, and T4: 500 mg L-carnitine per kg diet) with 5 replications and sampling twice (semen collection) with an in-terval of 14 days. The collected semen was immediately evaluated for motility parameters and sperm qual-ity traits. The results showed that there is no significant difference between the levels of 250 and 500 mg of L-carnitine in semen parameters, but there are significant differences with other groups (P≤0.05). Semen collection time did not affect sperm parameters (P≤0.05). In conclusion, the addition of L-carnitine at a rate of 250 mg/kg diet can improve motility parameters and sperm quality traits in the Cobb rooster. Manuscript profile