In this paper, we report morphology tunable self-aggregates of poly(amino acid)-drug conjugates. Amphiphilic drug-grafted polymers were synthesized by grafting hydrophobic phytosphingosine (PHS) onto two different hydrophilic poly(amino acid)s backbones, and the hydrophilic/hydrophobic ratio were controlled by varying the number of grafted drugs. The amphiphilic poly(amino acid)-g-PHS formed self-aggregates in aqueous solution, and morphology transitions of the self-aggregates from sphere to ellipsoid to cylindrical micelles were observed with increasing number of grafted phytosphingosines. Morphologies of self-aggregates were further confirmed by small angle neutron scattering, showing that the obtained self-aggregates consisted of a thin poly( amino acid) shell and a PHS core. The morphological changes of PHS-grafted poly(amino acid) were interpreted using geometrical changes of building blocks arising from the decrease of the hydrophilic part per PHS with increasing number of PHS grafts. (C) 2016 Elsevier B.V. All rights reserved.