The present study was conducted to investigate the effects of maturity stages on the chemical composition, in vitro gas and methane production, metabolic energy and organic matter digestibility for eleven Astragalus species widely encountered over the rangelands and intensely grazed by ruminants. Astragalus samples were collected from the rangelands at three different stages namely as before flowering, flowering and bear fruit stages. Dried samples were then subjected to various chemical analysis. Effects of Astragalus species and maturity stages on chemical composition, in vitro gas and methane production, metabolic energy and organic matter digestibility were found to be quite significant (P < 0.001). Acid detergent fiber (ADF) and neutral detergent fiber (NDF) ratios increased, while the crude protein, crude ash, crude oil, condensed tannin contents, gas and methane production levels decreased with the progress of maturity stage. It can be suggested that grazing was more favorable at before flowering or flowering stages of Astragalus species because of high crude protein and metabolic energy content of plant at these stages. Also, although all Astragalus species were considered as a quality feed source for ruminants, endemic Astragalus oocephalus and Astragalus longifolius species were prominent with their superior nutritive properties.