Fodder radish is widely used as a livestock supplement, however, the nutritional value of fodder radish under different water conditions remains insufficiently understood. This study aimed to assess the chemical components and in vitro, ruminal dry matter degradability of two fodder radish genotypes (Endurance and Line 2) subjected to three irrigation regimes: well-watered (W1), moderate water stress (W2), and severe water stress (W3). The analysis revealed statistically significant effects of the main factors on the chemical composition and estimates of fodder radish leaves and tubers, particularly in terms of Crude Protein (CP) and Ether Extract (EE) across genotypes. Both Endurance and Line 2 leaves exhibited interaction effects on N, P, Ca, Mg, K, Na, Fe, Zn, Cu, Mn and Al. Meanwhile only Na, K, Zn, and Cu were affected in tubers. Endurance tubers, specifically, displayed significantly higher (p < 0.05) CP content, with Line 2 tubers showing the highest CP content under W1. Furthermore, Endurance leaves had higher levels of Neutral Detergent Fibre, EE, and Non-Structural Carbohydrate (NSC) compared to Line 2 leaves under W1. Notable differences in tuber fibres were found, specifically in Acid Detergent Fibre for Endurance, with W3 exhibiting a higher concentration level. Both genotypes displayed higher NSC under W3. Significant variations in macro and mmicro minerals were observed between water levels in both genotypes. In terms of in vitro degradability during the 24 h and 48 h incubation periods, all treatments met the acceptable level of 60–80 %. Regardless of water regimes, both Endurance and Line 2 showed nutrient concentrations meeting the minimum requirements for optimal animal production. Though, Line 2 exhibits significantly higher nutritional value and in vitro ruminal dry matter degradability than Endurance, evident in both leaves and tubers. Notably, moderate water stress conditions yielded better nutritional quality and in vitro ruminal dry matter degradability compared to both well-watered and severe water stress treatments. This suggests that applying 180–220 mm of water per season can also yield better nutritive value of these genotypes.