PROBLEM TO BE SOLVED: To provide a microorganism-controlling agent that exerts excellent microorganism-controlling actions, in particular, an antibacterial action, an algicidal action and an action of preventing biofilm formation and yet shows suppressed metal elution, a miticidal composition that exerts an excellent action of suppressing the infestation and growth of mites, a mite-controlling material and a mite-controlling method.SOLUTION: The microorganism-controlling agent contains platinum particles and particles of a metal other than platinum. The metal particles comprise at least one selected from the group consisting of silver particles, copper particles, nickel particles, and zinc particles. In the microorganism-controlling agent, the platinum particles and the metal particles may be carried on a support. The platinum particles and the metal particles have a mean particle size of 0.1 to 1000 nm and are carried on the support in an amount of 0.01 to 20,000 ng/cm.SELECTED DRAWING: None【課題】微生物防除性能、特に抗菌性能、防藻性能やバイオフィルム形成抑制性能に優れ、しかも、金属の溶出が抑制された微生物防除剤、並びに、ダニの発生及び増加を抑制する性能に優れ、殺ダニ組成物、防ダニ部材及び防ダニ方法を提供。【解決手段】白金粒子と、白金以外の金属粒子とを含む微生物防除剤。前記金属粒子が銀粒子、銅粒子、ニッケル粒子及び亜鉛粒子から選ばれる少なくとも１種を含む。また、前記白金粒子及び前記金属粒子が基材上に担持されていてもよい微生物防除剤。白金粒子及び金属粒子の平均粒子径が０．１～１０００ｎｍのナノ粒であり、０．０１～２０，０００ｎｇ／ｃｍ２で基材に担持されている微生物防除剤。【選択図】なし
