An object of the present invention is to provide a nucleic acid delivery carrier composition of low toxicity and high safety, the carrier composition, when used to administer a nucleic acid such as an siRNA into an animal-derived cell or organism, being capable of delivering efficiently the nucleic acids into the cells while protecting it from being degraded； and a nucleic acid deliver composition containing the carrier and a nucleic acid. The carrier composition for delivery of a nucleic acid is prepared by mixing (A) a cationic lipid having a steroid skeleton with (B) a tertiary ammonium salt-type cationic lipid. The nucleic acid delivery composition is prepared by mixing the nucleic acid delivery carrier with a nucleic acid.本發明目的在於提供將siRNA核酸投藥於動物來源細胞或生物時，可保護核酸免於分解、並可有效率地使其遞送到細胞內之低毒性核酸遞送用載劑組成物、及含有該載劑組成物與核酸之核酸遞送用組成物。本發明係組合(A)具有類固醇核之陽離子性脂質、及(B)第4級銨鹽型之陽離子性脂質並將之混合，調製核酸遞送用載劑組成物。又，本發明係混合該核酸遞送用載劑組成物與核酸，調製核酸遞送用組成物。
