Legume seeds have high nutraceutical appeal and they can produce a balanced food when mixed with cereals. There has been little research on developing extrudate snacks with special health-enhancing characteristics. Therefore, the aim of this study was to estimate the quantitative changes in the nutritional, physicochemical and phytochemical properties of rice–horse gram flour blend extrudate. Rice and horse gram flour blends were prepared in 70:30 proportions and were subjected to extrusion cooking. The effect of feed moisture (14–18%) and barrel temperature (140–180°C) on the nutritional, physicochemical (expansion, density, water solubility index, water absorption index and hardness) and phytochemical (total phenolic content [TPC] and total flavonoid content [TFC]) properties were studied. Antioxidant capacity was measured using the ABTS assay. High die temperature combined with low feed moisture was suitable for obtaining well expanded snacks having desirable density and hardness values. A significant decrease in TPC and TFC was observed upon extrusion and a further decrease of 8–29% in TPC and 13–27% in TFC was observed when feed moisture and die temperature were increased. Antioxidant activity increased upon extrusion and this increase was the highest (36–49%) at 180°C with 18% feed moisture. This study demonstrated the potential for production of low-cost expanded snacks with improved antioxidant capacity.