Probiotics, enzymes, organic acids, oligosaccharides, antioxidants, and other functional materials are actively being explored as alternatives to antibiotics. Probiotics include live beneficial microorganisms that colonize the intestinal tract and competitively inhibit attachment and growth of harmful microbes. Probiotics also increase feed efficiency by assisting in nutrient absorption and digestion. The current study was conducted in order to evaluate the effect of a new probiotic, CS-A, as a dietary supplement of a fermented product on growth performance, feed intake, and feed conversion efficiency in broiler chickens, and to evaluate its value as an alternative for antibiotics used as a feed additive. Antibacterial and anti-inflammatory effects of CS-A were investigated in vitro and the in vivo effects of a constant concentration of supplemented CS-A on growth rate and feed efficiency were evaluated. In addition, the safety of CS-A was assessed by examination of common symptoms and mortality. Determination of minimal inhibitory concentration revealed an excellent antibacterial effect of CS-A. Cytotoxicity was low and anti-inflammatory effects were achieved at the effective concentration of CS-A. Supplementation with 0.1% CS-A resulted in a feed efficiency score of 1.84 in broilers, compared to 2.00 in the control group. There were no adverse clinical findings, necropsy findings, hematology, and altered serum biochemistry parameters, and no mortality. Thus, it is concluded that CS-A is safe and effective as a feed additive.