As shown in Table 2, xylanase supplementation of the basal diet at the recommended level (1X) did not have an effect on performance parameters and bone mineralization at 18 d of age. However, it did depress BW and FCR when its supplementation level further increased to 2X. The interaction between phytase and xylanase inclusion rate was not significant (P > 0.05) for broiler performance or toe and tibia mineralization rates.