Phaffia rhodozyma is a species of yeast that produces the carotenoid pigment astaxanthin (AST), which exhibits a wide variety of biological activities in animals. A total of 432 1-d-old male broilers (Arbor Acres) was used in a 4-wk trial. Birds were allotted to 1 of 3 corn-soybean meal-based diets supplemented with 0 mg (CON, basal diet), 1,000 mg (CON + AST production 0.1%) or 2,000 mg (CON + AST production 0.2%) P. rhodozyma yeast per kg feed. There were 9 replicate cages per treatment, with 16 broilers per pen. Nine broilers were randomly selected from each treatment (1 bird per cage) for sampling on d 28. Statistical analysis was performed using the mixed models analysis procedures in SAS, with AST treatment and pen serving as the fixed and random effect model terms, respectively. In addition, orthogonal comparison was conducted using polynomial regression to measure the linear and quadratic effect of increasing dietary concentrations of supplemental AST production. Alpha level of significance was set at P < 0.05. The inclusion of yeast-AST in feed improved body weight gain in a linear fashion with increasing AST concentration (969, 989, 1024 g) in the finisher period and the overall experimental period (1377, 1401, 1439 g). Furthermore, yeast supplementation reduced feed conversion ratio (1.650, 1.603, 1.562) in the finisher period, and tended (P < 0.10) to reduce feed conversion ratio for the overall experimental period (1.588, 1.554, 1.525). The yeast-AST supplemental diet had no effect on breast muscle color or pH, and water holding capacity values. Treatments with yeast-AST reduced ammonia emission in a linear fashion (17.98, 14.42, 14.32 ppm). This study demonstrated that yeast producing AST supplementation has a positive effect on BWG and FCR in the finisher period and the overall experimental period. It is possible that yeast-AST might maintain and promote the growth of a beneficial microbial population in fast-growing broilers. Moreover, there was an effective reduction in the fecal ammonia in response to treatment with yeast-AST. Ammonia is considered the most harmful gas to livestock, and can reduce daily weight gains and feed utilization.