A radiation-sensitive resin composition comprising (A) a photoacid generator such as 2,4,6-trimethylphenyldiphenylsulfonium 2,4-difluorobenzenesulfonate or 2,4,6-trimethylphenyldiphenylsulfonium 4-trifluoromethylbenzenesulfonate and (B) a resin having an acetal structure typified by a poly(p-hydroxystyrene) resin in which a part of hydrogen atoms of phenolic hydroxyl groups have been replaced by 1-ethoxyethyl groups, 1-ethoxyethyl groups and t-butoxycarbonyl groups, or 1-ethoxyethyl groups and t-butyl groups. The resin composition is sensitive to deep ultraviolet rays and charged particles such as electron beams, exhibits excellent resolution performance and pattern shape-forming capability, and suppresses a nano-edge roughness phenomenon to a minimal extent.