This study investigates the novel effect of poly(lactic acid) (PLA) optical purity on PLA/liquid natural rubber (LNR) blend films fabricated by solution casting. An investigation was conducted to examine how different levels of PLA optical purity affect the mechanical, structural, morphological, thermal, and barrier properties of PLA/LNR films. Infrared spectroscopy analysis revealed that the D‐isomer content of PLA significantly affected the chemical interactions between the LNR and PLA. The favorable chemical interaction between the LNR and PLA with a high D‐isomer content also increased the elongation at break by 300%. Morphological investigations proved that the chemical interaction also improved the dispersion and reduced the size of the LNR droplets formed in the PLA matrix. Notably, while low D‐isomer PLA blends showed decreased crystallinity ( X c ) upon LNR addition, high D‐isomer PLA blends exhibited increased X c by 460%, leading to a 42% increase in oxygen transmission rate. Additionally, hydrolytic degradation of high D‐isomer PLA increased by 259% with increasing LNR content. Overall, optical purity of PLA plays an important role in determining the properties of PLA blends.