PCPDTBT, a copolymer of cyclopentadithiophene and benzothiadiazole, is a locally ordered low-bandgap donor-acceptor conjugated polymer that has been used as a hole-transport material for polymer blend solar cells. In this study, the short-range order structure of PCPDTBT in spin-coated PCPDTBT/conjugated polymer blend films has been characterized to elucidate aggregation behaviors that arise when a locally ordered conjugated polymer is blended with other polymers. UV- vis absorption spectroscopy and grazing-incidence wide-angle X-ray scattering measurements revealed that short-range ordering of PCPDTBT is promoted when it is diluted in an amorphous conjugated polymer matrix, poly(3-methyl-4-hexylthiophene-2,5-diyl) (P3M4HT). In a PCPDTBT/P3M4HT blend film with 10 wt % PCPDTBT, the fraction of PCPDTBT chains that form aggregates increases from 51% (in neat film) to 78%, and the correlation length of the ordered PCPDTBT chains extends from 4.6 nm (in neat film) to 7.7 nm in the chain backbone direction. The polymer matrix-assisted ordering can be explained in terms of suppression of both undesired overlap and interpenetration of PCPDTBT chains; both processes can derange the self-aggregated single-chain order of PCPDTBT. This short-range ordering enhancement would be significant for the design of efficient charge carrier transport in thin-film devices such as polymer/polymer blend solar cells that use low-bandgap donor-acceptor conjugated polymers with various blend ratios as hole- and electron-transport materials.