Tuning the aggregation and crystalline properties of polymers is critical for realizing all-polymer solar cells (all-PSCs) with optimal blend morphology and high power conversion efficiency (PCE). In this study, a series of polymerized small-molecule acceptors (PSMAs) is developed to investigate important relationships among their crystalline/aggregation properties, the blend morphology, and the device performance of the resulting all-PSCs. A series of PSMAs (regiorandom (RRd)-C12, RRd-C20, RRd-C24, regioregular (RRg)-C20, and RRg-C24) with simultaneously-engineered i) side chain lengths of C12, C20, and C24, and ii) backbone regioregularities of RRd and RRg are synthesized to regulate their crystalline/aggregation properties. As a result, the highest PCE of 15.12% is obtained with all-PSCs based on RRg-C20 PSMA having regioregular backbone and optimal side chain length, attributed to high PSMA crystallinity and electron mobility as well as optimal blend morphology with a polymer donor. Thus, this study demonstrates the importance of simultaneous engineering of the backbone regioregularity and side-chain structures of PSMAs to enhance electron mobility, optimize blend morphology and, thus, achieve highly efficient all-PSCs.