A total of 144 (72 barrows + 72 gilts) crossbred pigs were used to determine the effect of feeding supplemental phytase and ideal dietary amino acid ratios in covered barley (CB) or hulless barley (HB)-based diets on growth performance, carcass quality, and excretion of phosphorus and nitrogen in manure during the grower and finisher periods. The three experimental grower and finisher diets were: 1) control diet (CB or HB) with Ca:P ratios according to National Research Council (NAS-NRC 1988), 2) the same as diet 1 but without added inorganic P, but supplemented with phytase (Novo Nordisk, Denmark) at 500 FTU kg-1, 3) the same as diet 2 with reduced dietary protein level, and supplemental amino acids lysine, threonine, and methionine to provide ideal dietary amino acid ratios of 0.70 for threonine to lysine and 0.30 for methionine to lysine. All diets were fed as pellets ad libitum in self-feeders with free access to drinking water. The ADG was not different (P > 0.10) between CB and HB or among the treatment diets during the grower, finisher and combined grower-finisher periods. The gain-to-feed ratios were higher (P < 0.01) for HB than for CB diets. They were also higher (P < 0.05) for diet 3 than for diet 1 during the finisher and combined grower-finisher periods. Carcass index and dressing percent were not different (P > 0.10) among the treatment diets. Supplemental phytase decreased (P < 0.05) the excretion of P during both grower and finisher periods. The combination of phytase and dietary ideal amino acid ratios decreased (P < 0.01) the excretion of both P and N. The ammonia and hydrogen sulphide production in stored liquid manure was not different among the diets.