The present invention relates to a nanocomplex, and a pharmaceutical composition, a drug delivery system and a drug delivery method using the same. The present nanocomplex consists of a nucleic acid molecule, a monocationic drug and a biocompatible polymer surfactant, and not only has a hydrodynamic size of 10 nm or less, but uniformly distributes as a colloidal form in an aqueous environment. In addition, the nanoscale colloidal formulation of the present invention could protect the nucleic acid molecule from a nuclease (for example, serum nucleases) rich in a physiological environment through the formulation of a stable monocomplex, and provide improvement of cell penetration and in vivo delivery via a micellar structure as well as further protection of the nucleic acid molecule by a micellar passivation. Therefore, the present nanocomplex and a composition and system using the same can deliver an active ingredient (for example, a nucleic acid molecule and monocationic drug) into a cell/tissue of interest in a stable manner, and may be effectively applied for treating or detecting diverse disorders (practically, cancers).