The conventional silk fibroin(SF)films obtained by casting from SF aqueous solution are amorphous,and easily dissolved in water.This defect limits the practical use of SF films in biomedical field.A new water-insoluble silk fibroin film(an SF-FA film)could be simply prepared by casting from SF formic acid solution.The physical properties and moisture permeability of SF-FA films were examined.The results show that the SF-FA film swollen in water exhibits outstanding pliability.The weight loss of SF-FA films in water is also very little.The unique physical properties for the SF-FA film in the wet relate to the intrinsic structure of the fibroin film.The cell viability of rat embryo dermal fibroblasts seeded on the control films and the SF-FA films was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)assay.Results show that the optical density(OD)value of the SF-FA film is almost the same as that of the conventional SF film treated with alcohol,therefore,the SF-FA film has good cell compatibility.In addition,the SF-FA film is also a biodegradable material.Because of their good transparency,it is helpful in study of clinical experiment with the SF-FA films. The conventional silk fibroin (SF) films obtained by casting from SF aqueous solution are amorphous, and easily dissolved in water. This defect limits the practical use of SF films in biomedical field. A new water-insoluble silk fibroin film (an SF-FA film) could be simply prepared by casting SF formic acid solution. The physical properties and moisture permeability of SF-FA films were examined. The results show that the SF-FA film swollen in water showed outstanding pliability. The weight loss of SF- FA films in water is also very little. The unique physical properties for the SF-FA film in the wet relates to the intrinsic structure of the fibroin film. The cell viability of rat embryo dermal fibroblasts seeded on the control films and the SF-FA films was evaluated by 3- (4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide (MTT) assay. Results show that the optical density (OD) value of the SF-FA film is almost the same as as that of the conventional SF film treated with alcohol, therefore, the S F-FA film has good cell compatibility. In addition, the SF-FA film is also a biodegradable material. Since the good transparency, it is helpful in study of clinical experiment with the SF-FA films.