In this communication, a novel "self-templating" strategy was used to prepare uniform and biocompatible nanocapsules by the addition of a reduction agent (i.e., DTT) into a solution of highly monodispersed PICmicelles bearing a heterodetachable PEG corona. PEG chains were released from PICmicelle shells following disulfide reduction which leads a spontaneous and drastic morphology evolution from micelles to vesicles induced by the decrease of the PEG weight fraction. Formation of uniform nanocapsules with controllable capsule size was achieved by careful control of the micelle composition and molecular weight of homo-P[Asp(DET)].