The development of bio-based and biodegradable materials is critical for reducing environmental impact and addressing global challenges associated with the extensive use of plastics in packaging applications. In this study, linear oligomers of butylene succinate (OBS) with three different molecular weights were synthesized using succinic acid (SA) and 1,4-butanediol (BDO), both monomers derived from biomass. The synthesized fully bio-based OBS samples were characterized in terms of their molecular structure, degree of polymerization, crystallinity, and thermal properties, showcasing their potential as additives for biopolymers in food packaging. Oligomers with weight-average molecular weight (M) values of 2050 g·mol (OBS-L), 16,150 g·mol (OBS-M), and 33,147 g·mol (OBS-H), and Ð values in the 1.7-1.8 range were successfully synthesized. The results showed that the thermal degradation stability of OBS slightly increased, while the crystallinity decreased with increasing molecular weight. Furthermore, the analysis of the evolution of the lattice parameters suggested that oligomers with shorter chains favored crystal organization, resulting in a crystal unit cell with denser packing.