The present invention provides a cationic lipid which is able to be used for nucleic acid delivery to the cytoplasm. A cationic lipid according to the present invention is, for example, a compound represented by formula (1a) or a pharmaceutically acceptable salt thereof. (In formula (1a), each of L1 and L2 independently represents an alkylene group having 3-10 carbon atoms； each of R1 and R2 independently represents an alkyl group having 4-22 carbon atoms or an alkenyl group having 4-22 carbon atoms； X1 represents a single bond or -CO-O-； and ring P represents one of formulae (P-1) to (P-5).) (In formulae (P-1) to (P-5), R3 represents an alkyl group having 1-3 carbon atoms).本發明提供一種能夠用於細胞質之核酸傳遞之陽離子性脂質。本發明之陽離子性脂質例如為下述式（1a）所表示之化合物或其藥學上容許之鹽。 〔化104〕〔式中，L1及L2分別獨立地表示碳數3～10之伸烷基，R1及R2分別獨立地表示碳數4～22之烷基或碳數4～22之烯基，X1表示單鍵或-CO-O-，環P表示下述式（P-1）～（P-5）之任一者〕 〔化105〕〔式中，R3表示碳數1～3之烷基〕。
