Recently, agricultural by-products, for instance, corn husks, oat husks, or cocoa shells, have gained attention as a source of cellulose fibers and fillers because they can save the land and other natural resources required to grow fiber crops. It has to be noted, however, that textile processing, for example, shearing, is also a source of waste fibers. Our study focuses on utilization of waste cotton fibers, amassed during shearing of textiles, as a filler for polylactide (PLA). PLA composites with 10-30 wt% of waste cotton fibers were prepared and their thermal and mechanical properties were studied. The composite with 30 wt% of fibers exhibited markedly higher storage and loss moduli as compared with neat PLA; at 25 degrees C the storage moduli increased by 53% whereas the loss modulus increased by 76%. In addition, the yield strength was slightly improved, by 11% at 25 degrees C. Although the composites were thermally less stable than neat PLA, their 5% weight loss temperature remained high, about 300 degrees C. POLYM. COMPOS., 35:747-751, 2014. (c) 2013 Society of Plastics Engineers