The synthesis conditions of fibrous calcium sulfate hemihydrate were investigated by using phosphogypsum and calcium sulfate hemihydrate. The unstable organogel was deposited by adding methanol to the saturated solution with gypsum at ageing temperature, and it was crystallized to fibrous gypsum hemihydrate while methanol was removed by rapid filtrating. In case of using calcium sulfate hemihydrate, fibrous $eta$-calcium sulfate hemihydrate was formed by adding methanol of 67% to saturated solution at 6$0^{circ}C$ and ageing for 5 minutes and filtering with suction. Minor components in phosphogypsum did not affect the reaction.