This research was conducted to determine the effects of feeding different P levels with and without phytase supplementation on broiler growth performance, bone breaking strength (BBS), and P excretion. An experiment with 4 trials was conducted with 7,840 Ross x Ross straight run broilers. For each trial, 1,960 broilers were allotted on d 0 to 4 treatments with 7 replications per treatment with 70 broilers per replication. The broilers were fed a 4 period feeding program consisting of starter (0 to 14 d), grower (14 to 32 d), finisher (32 to 41 d), and withdrawal (41 to 50 d) periods. For each trial, the same pen was used continuously for each treatment/replication combination, and the litter was not removed between trials. Broilers were fed a control diet (0.43, 0.40, 0.36, or 0.32% nonphytate P (nPP) in the starter, grower, finisher, and withdrawal periods, respectively), a low Ca and P (LCaP) diet with a 0.05% reduction in nPP in each period, and these two diets supplemented with 600 phytase units/kg (nPP was reduced by 0.094% in diets with phytase). Diet did not affect (P > 0.10) broiler performance in the starter or withdrawal periods. Generally, both phytase addition and the LCaP diet decreased some aspects of growth performance during the grower and finisher periods. There was no main effect of phytase on BBS, but BBS was decreased in the broilers fed the LCaP diet with phytase addition (nPP x Phy, P < 0.01) in the grower period, and BBS was decreased in finisher (P < 0.02) and withdrawal (P < 0.01) periods for broilers fed the LCaP diet. Total P (TP), soluble P (SP), and reactive soluble P (RSP) were decreased (P < 0.04) in the litter of broilers fed the LCaP diets. Total P was decreased (P < 0.01) in the litter of broilers fed phytase, but SP and RSP were not affected (P > 0.10) by phytase. These data indicate that phytase supplementation at 600 phytase units/kg reduces growth in some periods, has no effect on BBS, and that phytase reduces TP but not SP or RSP in the litter.