Abstract: The present invention relates to a microbiocidal mat to be installed at the entrance of a clean zone in a biochemical plant, a hospital or a like facility, the mat comprising a mat body 1 containing an alkaline compound 5 as a microbicide. The mat body may further contain a surface active agent and/or a water-retentive agent, the water-retentive agent comprising a substance which is stable against water and has deliquescence. Where the mat body 1 contains the compound and the agents in powdery crystallized states, the mat body 1 is used in a wet state by supplying water thereto after the mat is installed at the entrance. When the mat body 1 is supplied with water, the alkaline compound is dissolved in water within the mat body 1 so that the mat body 1 is imparted with microbiocidal activity.