With growing environmental awareness, ecological concerns and new legislations, natural fiber-reinforced plastic composites have received increasing attention during the recent decades. The natural fiber composites have many advantages over traditional glass fiber composites, including lower cost, lighter weight, environmental friendliness, and recyclability. This article reports the findings of the studies done on a new fiber, hitherto unexplored, extracted from Saccharum munja grass. The extracted fibers were further treated using sodium hydroxide to improve its performance in composites. Both treated and untreated fiber-reinforced composites were prepared by hand lay-up process using unsaturated polyester resin. Mechanical properties and thermal behavior of the composites were evaluated. The improvement in properties was found for alkali-treated fiber composites. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40829.