Submicrometer‐scaled (subμ‐) self‐assembled materials have been developed based on polyion complex (PIC) formation, in particular for biomedical‐applications. However, sufficient stability under physiological conditions is required for their practical use. In this study, PIC formation behavior is examined using a block aniomer, poly(ethylene glycol)‐b‐poly(aspartic acid), and homocatiomers, poly(l ‐lysine) (LPK) and dendritic poly(l ‐lysine) (DPK) with different generations, to elucidate the contribution of the dendritic architecture to stability enhancement. LPK‐based PIC shows a subμ‐vesicular structure only at 25 °C in the absence of NaCl; in contrast, DPK‐based PIC forms a subμ‐structure under physiological salt concentration and temperature conditions, even when the number of charges of a single molecule is much smaller than that of LPK. Moreover, the formation of subμ‐vesicular and ‐spherical micellar structures is dependent on DPK generation. Thus, the molecular backbone architecture of the PIC component plays an important role not only in expanding the preparation conditions and enhancing stability, but also in controlling the self‐assembled structures, mainly due to the spatially restricted structures of dendrimers.
