We determine the mobility of positive and negative charge carriers in a soluble green-emitting alternating block copolymer with a methoxy bi-substituted conjugated segment. The negative charge carrier mobility of 6 x 10-11 cm /V.s is directly determined using space-charge-limited current analytical expressions. Positive charge carrier transport is also space-charge-limited, with a mobility of 1 x 10-8 eV. The electron trap distribution is exponential, with a characteristic energy of ~ 0.12 eV. A hole trap with energy ~ 0.4 eV was observed. This copolymer is used as emissive material in organic light-emitting diodes that present brightness of ~ 900 dc/m² at 12.5 V.