A pot experiment was conducted to evaluate the relative agronomic effectiveness (RAE%) of a Syrian phosphate rock when it is added alone and as mixture with elemental sulfur with three different ratios (PR:S) (2:1) (5:1) (8:1) and compared with triple superphosphate. The main results of this study showed that Ain Layloun phosphate rock was not effective for direct use by Rye grass when used alone, but it became effective when mixed with elemental sulfur. The relative agronomic effectiveness was varied following mixing ratios, it was 50%, 76% and 87% in (8:1), (5:1) and (2:1) (PR:S) mixing ratios respectively. This is due to the increase of available soil phosphorus content which is related to the increase of phosphate rock solubility due to decrease of pH derived from oxidation of sulfur by Thiobacillus spp.