A series of bio-based poly(propylene-co-2-methyl-1,3-propanediol 2,5-furandicarboxylate) (PPMF) copolyesters, with various compositions from poly(propylene 2,5-furandicarboxylate) (PPF) to poly(2-methyl-1,3-propylene 2,5-furandicarboxylate) (PMePF), were synthesized by conventional melt polymerization. The effects of the substituent group to PPF on the thermal properties, mechanical properties, and gas barrier properties were analyzed by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), tensile testing, and the oxygen permeation test. The introduction of the methyl group with a hydrogen atom altered the thermal behavior and gas barrier properties of copolyesters, suggesting that the glass temperature (Tg) and the melting temperature (Tm) were decreased as the 2-methyl-1,3-propanediol (MPO) content increased. PPF exhibited the highest Tm and Tg of 175.9 °C and 83.0 °C with a melting enthalpy (ΔHm) of 38.6 J g-1, and poly(2-methyl-1,3-propylene 2,5-furandicarboxylate) formed as an amorphous polyester. Moreover, the effect of a substituent methyl group on the barrier properties was attributed to β relaxation and fraction free volume, which could be raised by replacing the methyl group with a hydrogen atom for PPF, weakening the barrier properties.