This study was carried out to evaluate the effect of PrimaLac probiotic (based on lactic acid bacteria; LAB) addition and frequency of application on Cyprinus carpio blood serum factors and growth performance (weight gain). For this purpose, 84 fish with an average weight of 60 ± 10 g in 4 groups with 3 replications in each group were compared for 42 days. Control diet had not probiotic additive but treatments of 1, 2, 3 probiotic usages daily, every other day, on 2 successive days in every 4 days period of time, respectively. During the experiment period, feed intake and growth rate were recorded. At the end of experiment, experimental fishes were killed by dianthus powder and then were measured serum cortisol, albumin, and total protein. The average rates of total protein and albumin in group1 were increased (p < 0.05) and cortisol serum level decreased in all experimental groups compared to control group (p < 0.05). The average weight gain in all experimental groups that used probiotic, significantly increased (p < 0.05). Weight gain was increased in daily addition probiotic group compared to control and other experimental groups (p < 0.05). The result of this study had shown that use of probiotic based on LAB can affect on cortisol, albumin, total protein serum, and growth performance and also probiotic frequency of application can affect on probiotic efficiency.