Technical Abstract: Elephant grass (Pennisetum purpureum Schum.) is a new fast-growing alternative forage crop. However, salinity is a major concern for its production in the arid southwestern United States. This study was conducted in the arid Imperial Valley of S. California to evaluate salt tolerance of elephant grass. Salinity treatments were created in field plots irrigated with water possessing an electrical conductivity of 1.5,5,10,15,20, and 25 dS/m, respectively. Canopy spectral reflectance, temperature, plant height, leaf area index (LAI), chlorophyll - SPAD meter readings, and dry weights were measured over time. Results indicated that canopy reflectance in the near-infrared spectral region was reduced incrementally with increasing levels of salt stress. Canopy temperature increased with increasing salinity, especially at longer times after salinity treatment. Plant Height and LAI were reduced with increasing salinity. Biomass accumulation was reduced incrementally with increasing salinity. About 50% yield reduction was found when electrical conductivity increased from 5 to 25 dS/m. The study shows that elephant grass is sensitive to salt stress, and relatively low salinity must be maintained to achieve a high rate of growth and biomass production.