Numerous light rare earth elements (LREE) minerals containing Fe and P were processed by sulfuric acid roasting method, and the leaching solution mainly comprises LREE sulfate, Fe2(SO4)3, H3PO4, and H2SO4, however, the solubility data of LREE sulfates in this system is few. This work studies the solubility of LREE sulfates in independent LREE sulfate system RE2(SO4)3-Fe2(SO4)3-H3PO4-H2SO4 (RE = La, Ce, Pr or Nd) and mixed LREE sulfates system (La,Ce,Pr,Nd)2(SO4)3-Fe2(SO4)3-H3PO4-H2SO4 at different temperature (25-65 ℃) and concentrations of Fe2(SO4)3 (Fe2O3, 0-50.13 g/L), H2SO4 (0.5 mol/L), and H3PO4 (P2O5, 20.34 g/L) based on the industrial operating condition at low liquid and solid ratio 2:1. The solubility of each LREE sulfate in the independent system (La2O3, 12.25-20.88 g/L; CeO2, 41.93-62.35 g/L;Pr6O11, 37.34-56.69 g/L;Nd2O3, 26.60-37.63 g/L) is much higher than that of the mixed system (La2O3, 6.95-11.03 g/L;CeO2, 10.63-21.51 g/L;Pr6O11, 11.56-20.36 g/L;Nd2O3, 12.36-19.79 g/L) under the same other conditions. The results also indicate that, in the two systems, both Fe and the temperature have negative effects on the solubility of LREE sulfates. That may occur due to the complication reactions between the complexes of RESO4+and Fe(SO4)2-. However, the influence degree of temperature and iron concentration on the LREE sulfates solubility varies in the two systems and among different LREE species. This research is of theoretical significance for optimizing the conditions of the sulfuric acid process for recovering the LREE from the mixed LREE bearing minerals as well as the single LREE containing sec-ondary rare earth scraps.