Mercury concentration was quantified in liver, muscle, and primary feathers of pooled samples of Western Sandpiper (Calidris mauri) collected in December-January 2010 (wintering) and March-April 2011 (premigration) in Ensenada Pabellones and Bahía Santa María, Sinaloa, Mexico, to test for differences between sites, stages, tissues, and age-sex groups. During the winter, mercury concentrations were greater in individuals from Ensenada Pabellones than those from Bahía Santa María (0.81 ± 0.05 vs. 0.57 ± 0.05 mg/kg dry weight, respectively), and greater in liver than in muscle (0.89 ± 0.05 vs. 0.49 ± 0.05mg/kg dry weight, respectively). In the comparison between the stages, wintering birds had greater concentrations of mercury than those of premigration period (0.62 ± 0.05 vs. 0.48 ± 0.05 mg/kg dry weight, respectively). These mercury concentrations were lower than those found in other wintering sites in North America (mean = 4.4 mg/kg dry weight). Although these concentrations suggest that Western Sandpipers wintering on the coast of Sinaloa, Mexico, were being exposed to low mercury concentrations and had not accumulated mercury, it appears that mercury in their tissues decreased during the nonbreeding season. However, these conclusions are based on low numbers in some categories and require further work with individual, rather than pooled, samples.