Biodegradable polymers have attracted a great deal of attention in decades owing to the environmental concern and sustainability issue. Among them, poly(lactic acid) (PLA) is the most used biodegradable polymer which is derived from renewable resources and considered as non-toxic for humans and the environment. On the other hand, it is important for the food packaging films to have antibacterial properties, in addition to biodegradable properties. In this study, we tried to fabricate antibacterial PLA films by the addition of sub-micron chitosan (CS) particles which were prepared by ionic-crosslinking through the negative-charged tripolyphosphate (TPP) and the positive-charged CS chains under suitable pH values. The CS-TPP gel particles had an average diameter of 200 nm and were then blended into the PLA. Tensile mechanical properties and antibacterial properties of the prepared PLA/CS-TPP films were measured. The results showed that both Young’s modulus and antibacterial properties increased with the addition amount of CS-TPP particles. The inhibition efficiencies of the PLA film at 6 wt% CS-TPP for the E. coli and S. aureus could be increased to 21.7% and 23.8%, respectively, when compared to the control.