The shape of self-assembling polymerdrug conjugates, influencing the cellular uptake, is one of the important factors to be considered for effective drug delivery. In this study, we described synthesis of polymeric drug conjugates of different morphologies with phytosphingosine (PHS) as a hydrophobic model drug and poly(amino acid) as a hydrophilic host polymer. By varying the amount of PHS grafted to poly(amino acid), PHSpoly(amino acid) conjugates exhibited morphological transition from spherical to worm-like micellar aggregates in the aqueous media. We investigated the physicochemical properties of self-assembled structures in terms of hydrodynamic size, surface charge, and critical aggregation concentration. The anticancer therapeutic potency of these self-assembled structures was also discussed in terms of cellular uptake and cytotoxicity of prodrug micelles as a function of dose and time by in vitro cell study. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012