The experiment was carried out on 24 growing Polish Landrace pigs. The apparent digestibility of P from cereal grains (maize, barley, wheat, triticale, rye or mixture of barley with rye) and from diets containing cereals and 25% rapeseed meal (RSM) or 40% soyabean meal (SBM) was determined. The diets were unsupplemented or supplemented with microbial phytase (1000 FTU/kg). The digestibility of P was measured by an indirect method (with Cr₂O₃ as an indicator) in 129 individual collections. The activity of intrinsic phytase in maize and oil meals was low (no more than 180 FTU/kg DM) and was considerably higher in other cereals (from 750 FTU in barley to 2077 FTU/kg DM in rye). The apparent digestibility of P in barley, wheat, triticale and rye did not differ between species (average 37.1%) and was about 17% percentage points higher (P<0.01) than in maize. Although it was estimated that the effect of intrinsic and microbial phytase on digestibility of P was additive, plant phytase was 32 and 41% less effective than microbial phytase in diets with RSM and SBM, respectively. The intrinsic phytase content in cereal improved P digestibility in diets with RSM or SBM by 9.3-9.6% per 1000 FTU. Supplementation of diets with microbial phytase (1000 FTU) increased P digestibility by 13.7 and 16.3% in RSM and SBM diets, respectively. However, the increase in the content of digestible P by microbial phytase was similar (about 1 g/kg) in diets with both protein sources.