Factorial field experiment was conducted to evaluate response relationship between two local wheat genotypes (Triticum aestivum) and phosphorus soil test values. The M 0.5 NaHCO3 based (Olsen phosphorus) extractant was carried out on soils taken from the plots. The experiment was conducted at western region of Libya. Soil pH at the experimental site was 8.1 and the texture is sandy. The experiment was performed using a randomized complete block design (RCBD) method with three replicates for each treatment of phosphate fertilizer at concentrations of 0, 60, and 120 kg P2O5 ha-1 for both genotypes. Results were expressed by relative values (Relative Yield). Relative yield (RY) of the two wheat cultivars showed similar significant responses to both soil test values and the grain yield. Linear relationship between relative yield and the grain yield at 0 kg P2O5 ha-1 for both genotypes was found, whereas, non-linear relationship was noticed among treatments that received 120 kg P2O5 ha-1. Both the linear and non- linear relationship have explained by tendency curves and showed how both genotypes response to phosphate fertilizer