The present invention is aimed to provide a novel cationic lipid which can form lipid particles.According to the present invention, provided is a compound of formula I a lipid particle comprising the compound, a nucleic acid-lipid particle containing the lipid particle, and a medicament containing the nucleic acid-lipid particle as active ingredient.本發明之課題在於提供可形成脂質粒子之新穎陽離子性脂質。本發明之解決手段為提供式I所示之化合物:提供包含該化合物之脂質粒子,包含該脂質粒子之核酸脂質粒子,以該核酸脂質粒子做為有效成分之醫藥。