In an effort to find a safe and environmentally-friendly substance to mildew-proof silk cultural relics, this study examined the anti-mould effects, on modern natural silk under certain light conditions, of natamycin, a safe, internationally wide-used mould inhibitor, using the bacteriostatic circle method. This work showed that whether of not nisin was used as an adjunct, 500 [micro]g/g of natamycin (the minimum effective amount) worked very well to inhibit the growth of Aspergillus niger, Penicillium and Mucor; furthermore, it had no adverse influence on the color and the mechanical strength of white silk. Therefore the prospects for using natamycin as mould inhibitor in silk cultural relics seem good.