Short crosslink structure and amorphous nature are the major reasons for the poor performance of cured epoxidized soybean oil (ESO) thermosets. Herein, a biobased crystalline oligomeric poly(butylene succinate) (OPBS) with dicarboxyl terminal groups was used as a long-chained and crystalline curing agent to increase the segment length within crosslinking points and make the cured thermoset to crystallize. The molecular weight of OPBS affected the curing process significantly. The curing rate decreased with increase in the molecular weight of OPBS. Addition of 4-N, N-dimethylaminopyridine as a catalyst accelerated the curing rate efficiently. The crosslink density decreased gradually with increase in the molecular weight of OPBS. The segment length of OPBS had a strong influence on the physical properties of the cured thermoset. The crystallization enhanced gradually with increasing segment length of OPBS, which then resulted in considerable improvement in melting temperature, mechanical strength and heat resistance of the thermoset. With improved mechanical properties and heat resistance, the fully biobased ESO thermosets could find more applications. (C) 2017 Elsevier B.V. All rights reserved.