To achieve pH-controlled drug release, a drug-loaded yolk/shell structured microcapsule with poly (DEAEMA-Styrene) (PDS) as yolk and polystyrene as shell was prepared by an all-in-one method of solvent evaporation and emulsion polymerization. The as-prepared microcapsule, in which the yolk swelled through the PDS pH-sensitive tertiary amino protonation and hydrophobic-to-hydrophilic transition, triggered the drug releasing via controlling the pH value. The yolk-swell microcapsule exhibited a non-swelling morphology in acidic solution to avoid extra drug diffusion. In the case of the pH value decreased from 7.5 to 3.4, there was a noticeable increase in the visible light transmittance of the PDS solution. In addition, the PDS swelling ratio increased from 10.7 to 5.8 as the value decreased from 5.3 to 3.4. The amounts of cumulative drug release were found to be 4-fold and 7-fold higher at pH 3.4 and 5.3, respectively, than that at pH 7.5, which demonstrated excellent pH response of the microcapsules. The unique yolk-swell strategy in this work sets a stage for an effective pathway in controllable drug delivery. (C) 2017 Elsevier B.V. All rights reserved.