To obtain an antibacterial thermoplastic resin compsn. excellent both in antimildew, antialgal, and antibacterial properties and in transparency by compounding a transparent thermoplastic resin with at least one specific antibac terial agent.

Any transparent thermoplastic resin can be used if its total light transmission is 80% or higher. Suitable examples of the resin are a methacrylic resin, a styrene resin, an MS (methacrylate-styrene copolymer) resin, and a polycarbonate resin. As the antibacterial agent are used a nitrile- based one (e.g. a haloisophthalonitrile compd.), a pyridine-based one (e.g. a sulfonylhalopyridine compd.), a haloalkylthio-based one (e.g. a haloalkylthiosulfimide compd.), an organoiodine-based one (e.g. a iodosulfonylbenzene compd.), a thiazole-based one (e.g. an isothiazolin-3-one compd.), and a benzimidazole-based one. The agent is compounded in an amt. of 0.01-5wt.% of the resin.