Refined silk fibroin obtained from waste cocoons was dissolved in a mixture of ethanol and neutral salt (calcium chloride) solution and the solution thus obtained was centrifuged and then acidified with an organic acid after dialysis. The pH of the resulting solution was in the acid side of the isoelectric point (pl=3.8-3.9). Fibroin gelation was carried out in an air-conditioned room. The gel strength and gelling rate were investigated under different conditions such as pH and concentration of fibroin solution. Structural features were studied by electron microscopy and infrared spectroscopy.