A field experiment was established at the College of Agriculture Experimental and Research Farm at Dirab, south Riyadh, during 1995-1996 season to study the effect of sewage water irrigation, P and K fertilization on yield of alfalfa (Medicago sativa L; var. CUF101) and availability of P  and K  in the soil. Two different soils in textures were used in this study namely; loamy and sandy soils. The results showed that application of sewage water resulted in a significant increase in alfalfa dry weight under the various levels of P and K. Irrigation with sewage water gave significantly higher yield of alfalfa than that of well water, regardless of P and K treatments in both soils. Application of 50, 150, and 250 kg P ha^-1 gave significantly higher yield of alfalfa grown under well water irrigation. The percent increment in alfalfa dry weight were 16.0, 29.5 and 35.0% in loamy soil and 18.1, 24.3 and 37.3% in the sandy soil. In contrast, the rate of increase due to P application was less pronounced under sewage water irrigation. Application of K either at a lower rate (50 kg K ha^-1) or at a higher rate (100 kg ha^-1) resulted only in a minor increase in alfalfa yield. The results indicated that the effect of sewage water irrigation was conspicuous on available P content of the soil and resulted in a higher P plant content even if no P fertilizer was applied. Data for available K in the soil indicated a significant decrease in K level regardless of K addition.