Amaranths (Amaranthus L.) are multi-use crop species known for their nutritional quality and tolerance to salinity stress. As soil salinity has become an increasing issue globally, we conducted a study to test the salinity tolerance of one cultivar of Amaranthus retroflexus L. (Redroot pigweed). The plants were grown for 30 days in pot culture conditions at different salinity levels: non-saline, slightly saline, moderately saline, highly saline, and extremely saline (using two different rates: extreme1 and extreme2. We assessed various growth parameters including plant height, stem diameter, root, stem and leaves fresh (FW) and dry weight (DW), water content (WC), photosynthesis rate (Pn), transpiration rate (E), water use efficiency (WUE), chlorophyll content index (CCI), nutrient content, phytodesalination potential, salt tolerance index (STI), and vegetation indices. Our findings indicated that at slight to moderate levels of salinity, growth parameters and other factors, such as STI and vegetation indices, were less affected compared to higher levels of salinity for A. retroflexus L.