In recent years, the home meal replacement (HMR) market has expanded and the consumption of ready-to-heat (RTH) rice has significantly increased. In this study, RTH rice products containing seaweed were prepared with different types of grain: white rice, a mixture of white rice and barley, barley, and mixed grains. The control was a commercial RTH white rice without seaweed. The proximate components, total dietary fiber, in vitro starch digestibility, and antioxidant activity were compared. The ash content of the RTH seaweed rice was higher than that of the control (P<0.05). The total dietary fiber of the RTH seaweed rice was in the range of 1.03-6.57%, which directly impacted the in vitro starch digestibility. The in vitro antioxidant activity including total phenolic content, reducing power, DPPH (2,2-diphenyl-1-picryl-hydrazyl) and ABTS+ (2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid) radical scavenging activity of the seaweed rice with barley and the white rice/barley mixture was greater than that of the other rice products (P<0.05). These results indicate that the in vitro digestibility and antioxidant activity of the HMR RTH seaweed rice were greater than those of the control. In addition, when the RTH seaweed rice was prepared with barley, the functional activity improved.