The role of cheliped autotomy in the territorial behavior of the freshwater prawn Macrobrachium lar was analyzed to determine whether or not prawns modified their defended territory size based on cheliped autotomy. Territory size measurements were recorded for captive prawns interacting in artificial tank habitats and were logged according to the locations where agonistic encounters occurred and aggressive pressures were equal. All prawns used in this study were mid-intermolt males in the size class 9.0 ± 1.5 cm, with staged encounters occurring under three treatment conditions in which fully intact prawns were matched against animals possessing no chelipeds, one cheliped, or two chelipeds (fully intact). Separate experiments for each condition were completed with four prawns per tank per 14-day trial and were run a total of three times each. The defended territory size mean for the Control prawns (matched only against other intact animals) did not differ significantly from one quarter of the total tank area. The mean territory sizes for prawns within or between each treatment condition was significantly different. Prawns with one or two chelipeds autotomized each defended significantly smaller territories than other male prawns of equal size, but with both chelipeds intact. Our results show that the presence of chelipeds allowed the defense of larger territories compared with the territories defended by prawns with one or both chelipeds autotomized.