The solubility of calcium sulfate dihydrate (DH) and alpha-calcium sulfate hemihydrate in formamide aqueous solutions with 0-13 m formamide at temperatures from 303.15 to 363.15 K was measured by the dissolution equilibrium method. Formamide has a solubilization effect similar to the salt effect; the solubility of calcium sulfate dihydrate and alpha-calcium sulfate hemihydrate first increases significantly as the concentration of formamide aqueous solution increases. When the solubility reaches the maximum value, it decreases gradually. The modified Apelblat-Jouyban-Acree model shows good agreement with experimental values; hence, it may be suitable in describing the solubility of calcium sulfate dihydrate and alpha-calcium sulfate hemihydrate in the formamide aqueous solution at the temperatures ranging from 303.15 to 363.15 K under 88.35 kPa. On comparing the solubility of calcium sulfate dihydrate and alpha-calcium sulfate hemihydrate in the formamide aqueous solution, it was found that the solubility of alpha-calcium sulfate hemihydrate is lower than that of calcium sulfate dihydrate, being above 8.3418 and 3.7286 mol.kg(-1) when the temperatures are 353.15 and 363.15 K, respectively, which is beneficial to the conversion of calcium sulfate dihydrate into alpha-calcium sulfate hemihydrate.