This invention provides an anti periodontitis-causing microorganism agent that is highly safe and has no side effects and medical or dental materials that can make good water-insoluble excipients in addition to show antibacterial activity to periodontitis-causing microorganism by preparing the medical or dental materials with effective ingredients formed by at least one of protamin or its derivatives and hydrolysates, or from the complex of anionic high polymer and at least one of protamin or its derivatives and hydrolysates.藉由將魚精蛋白(protamine)、或其衍生物、水解物其中至少1種作為其有效成分，或將魚精蛋白、或其衍生物、水解物當中至少1種與陰離子性高分子的複合體作為有效成分，而製備醫療用或牙科用材料，可提供無副作用顧慮、安全性高的抗牙周病菌劑，且可提供除了顯示牙周病原菌的抗菌活性而且不溶於水且具良好賦形性之醫療用或牙科用材料。
