Abstract: A trail was conducted to investigate the effect of yeast (Saccharomyces cerevisiae SC47) utilization on the commercial layer hen’s performance. The experiment consisted of 5 diets (0, 0.25, 0.5, 0.75 and 1 g Yeast per kg diet) with five replicates each containing 15 laying hen’s hy-Line W36 from 25 to 78 week of age. The randomized complete design was used for this experiment. During the experiment egg weight, egg production (%), Egg Mass, feed conversion and egg quality were measured daily and every month, respectively. The data analyzed in five periods (25-32, 33-44, 45-58, 59-78 and 25-78 week). The result showed that using Yeast had no positive effect on feed intake in all of the periods (p<0.05). Duncan test showed that feed intake in 59-78 weeks for group of 3 (0.5 g kg-1 Yeast) was higher (102.06 g) than other groups. Egg production and average egg weight didn’t affected by using Yeast, but in 25-78 weeks, egg production in 4 and 5 treatments was 2.43 and 2.06% higher then control groups, respectively. In all of the periods egg mass in groups of 4 and 5 was higher than control but only in 59-78 weeks this difference was significant. In this period egg mass in 4 and 5 treatments was 6.98 and 8.42% higher than control. Yeast had no positive effect on feed conversion, but the group of 5 (1 g kg-1 Yeast) had a best feed conversion. Addition of Yeast in Commercial Layer hen diet was no effective on egg specific gravity, eggshell thickness, haugh unit, egg breaking strength and eggshell quality (p<0.05). Egg special gravity in group 2 was higher than group 3 (p<0.05). Haugh unit in group 5 was higher than other groups in all of the periods but this difference in 25-32 and 59-78 weeks was significant (p<0.05). The food intake cost in 25-78 weeks was 21, 11.9 and 17.65 Rials less for each kg egg in groups 3, 4 and 5, respectively.