A separator for a zinc bromine secondary cell which comprises a fine silica powder and a polyethylene blend having a viscosity average molecular weight of 350,000 to 2,000,000 and containing a polyethylene having a weight average molecular weight of 1,000,000 or more in an amount of 10 wt% to 80 wt%, wherein the weight ratio of polyethylene/fine silica powder is more than 1 and less than 1.5, and the ratio Si/C between the numbers of silicon atoms (Si) and carbon atoms (C) which are revealed on the surfaces not including a cut surface is not less than 0.01 and less than 0.2, as determined by X-ray photoelectron spectroscopy (XPS). |