Mixtures of ordinary superphosphate with fosforita tie Olinda (sedimentary origin) and apatita do Araxá (apatite type) were studied by chemical and mechanical analysis at various time intervals alter they were prepared. When the ground rock phosphate was in small percentage in the mixtures, the water-soluble content was higher than the theoretical calculated value from the components of the mixture. The increase of the water soluble fraction cannot be explained except by admitting that the superphosphate was not completely cured. Higher percentages of that component produces under the same conditions a mixture with a lower water-soluble phosphorus content than expected. At any percentage the time factor increased insolubility of this fraction. The variations of this P2O5 form were small. The citric-soluble phosphorus in the fosforita mixtures increased till 135 days after they were made and stabilized after this period. It seems that this form of phosphorus in the mixture is not affected by the amount of superphosphate. The citrate soluble P2O5 was studied only for fosforita because the data from apatite were scattered. This fraction for the former increased with time. It increased with higher percentages of superphosphate up to 50% and after it, it decreased. The citrate-soluble P2O5 variations were small. Grinding the mixtures had no effect on the water-soluble fraction except that met for no grinding. All pH determinations of the mixtures gave values below 5.0, decreasing with higher amounts of superphosphate. The apatita mixtures had a lower pH than the fosforita ones at same levels. The moisture content of the mixtures was lower than the theoretical value calculated from the phosphates. The mechanical analysis showed thad there was no variation in the apatita mixtures when compared to the theoretical value. In the fosforita the variations were small