The present invention provides nucleic acid-containing lipid nanoparticles comprising: a lipid (lipid A) which has three independent, optionally substituted hydrocarbon groups and a hydrophilic moiety having one quaternary ammonium group a lipid derivative or fatty acid derivative of a water-soluble polymer and a nucleic acid.本發明提供一種含有核酸之脂質奈米粒子,其包含:含有具有1個四級銨基之親水部及可具有取代基之獨立之三個烴基的脂質(脂質A)、水溶性高分子之脂質衍生物或脂肪酸衍生物、及核酸。