In this work, potato starch was hydrolyzed by acid (HCl) to form nanoparticles (SNPs) that were esterified with acid Rosin using a green heterogeneous catalyst based on Algerian montmorillonite clay known as “Magnhite”. It has a similar activity to the classical Brönsted (H 2 SO 4 ) and Lewis (Al 2 O 3 ) acids, which implies that it can replace homogeneous acid catalysts. Particular emphasis was devoted to investigate the influence of temperature, reaction time, and amount of catalyst on the degree of substitution (DS) on the reaction conditions to achieve a high DS. Fourier Transform Infrared analysis confirms the esterification of SNPs by the appearance of new bands at 1724 cm −1 assigned to ester group. X-ray diffraction and scanning electron microscopy indicate that the esterification reaction reduces the crystallinity while the morphology changes from SNPs nanoparticles to a completely destroyed form. Besides, the thermal stability of esterified SNPs has been slightly reduced compared to unmodified starch. The volumetric assay was used to evaluate the DS of the products and the effects of the rosin/glucose anhydrous acid unit in the molar ratio. It is found that DS increases with increasing the molar ratio and reaches its maximum value of 0.135 at a molar ratio of 4:1. Furthermore, antimicrobial activity study of SNPs esterified with rosin acid (DS between 0 and 0.141), revealed that the esterified SNPs were effective against all the tested bacterial strains. Moreover, the DS is directly proportional to the zone of inhibition. This research showcases the importance of the newly designed SNPs-Rosin formulation in the biomedical and food industries.