Mean annual air temperatures along the Antarctic Peninsula have increased ³2.9^oC over the past 50 years. Regional-climate models predict precipitation will also change. We examined how warming and increased precipitation alters decomposition of native vascular plant litter in the Antarctic tundra. Plant litter (Deschampsia antarctica and Colobanthus quitensis) was collected and placed into nylon mesh bags. We placed the bags into intact cores of living Antarctic vegetation located under heaters which supplied an additional 28 W m^-2 of infrared radiation or under dummy heaters. We supplemented half the cores weekly with an additional 25% of ambient precipitation. Canopy air and soil temperatures of cores under heaters averaged 1 and 2^oC higher than under dummy heaters. The experiment ran for 16 months, with half of the decomposition bags being removed for analysis after 4 months. There was a total mass loss of 25 and 22% from the initial sample weights of D. antarctica and C. quintensis after 4 months. Warming accelerated total mass loss by 22 and 31% over ambient conditions for D. antarctica and C. quintensis. Constituent analysis was performed on the decomposed litter to determine lignin, holocellulose, fat and lipid, and total organic carbon and nitrogen content. The increased mass loss under warming conditions appears to result primarily from the accelerated decomposition of holocellulose. Holocellulose concentrations were ~11% lower under warming for both species than under ambient conditions. Our results depict how regional warming may influence accumulation of soil organic matter and nutrient cycling in the Antarctic tundra.