Poly(lactic acid) (PLA) is an environmental friendly, bio-based polymer since it can be polymerized from lactic acid that can be obtained from renewable resources such as starch and sugar cane. PLA production has much lower carbon footprint compared to the petroleum-based conventional alternatives such as polystyrene, polypropylene, polyethylene, acrylonitrile-butadiene-styrene copolymer. Mechanical properties of PLA can be modified to replace these polymers by blending with additives and reinforcers. In our study, we aimed to improve the mechanical properties of PLA by blending the polymer with cotton gin waste to obtain fully bio-based and sustainable high performance material. Cotton is one of the most important agricultural crops used as a main clothing source. Cotton gin waste (CGW) is a side product occurring during cotton production which consists of cotton fiber, plant parts, leaves, soil and seeds. Similar to cotton, CGW is also a biodegradable material and since it contains cotton, it also exhibits its strength and durability. In this study, Poly(Lactic Acid) - Cotton Gin Waste composites were prepared by melt processing by an internal mixer. It is shown that addition of 5, 10 and 20% CGW into PLA significantly improves mechanical properties of unreinforced PLA. For instance, 10% addition of CGW increased flexural modulus by 41% and Izod impact strength 25% higher. Addition of 20% CGW into PLA resulted 51% increase in flexural modulus. The viscoelastic properties of the composites were investigated by using dynamic mechanical analysis and morphological characterization were performed by using scanning electron microscopy. With the improved properties, PLA-CGW composite can be a sustainable alternative for plastic parts of white goods applications.