Rice stalk fiber and rice husk ash are agricultural by-products, which are available worldwide in large quantities. There is, however, no information about suitability of the rice stalk fiber and rice husk ash combination for the production of fibercement composites in the open literature. This paper presents a parametric experimental study, which investigates the potential use of rice stalk fiber (as reinforcement) and rice husk ash (as cement replacement) admixtures for producing a lightweight fiber-cement composite as a building material. Three levels of fibrous materials, namely 10, 25 and 40 wt% were mixed with 0, 10 and 20 wt% of rice husk ash. Effects of these variable parameters on the mechanical (modulus of rupture, modulus of elasticity and internal bond) and physical properties (water absorption and thickness swelling) of the samples were studied. The results showed the effect of high-level replacement of rice stalk fiber with rice husk ash does not exhibit a sudden brittle fracture even beyond the failure loads, indicating high energy absorption capacity of the composites. Based on the findings of this work, the water absorption and thickness swelling of the composites increased with the increasing rice stalk fiber content in the samples from 10 to 40 wt%. On the other hand, modulus of rupture and modulus of elasticity of the boards were enhanced with increase in the percentage of rice stalk fiber. Boards having 25 wt% rice stalk fiber exhibited the highest internal bond strength. However, addition of rice stalk fiber and rice husk ash reduced the internal bond strength. Moreover, boards made with rice stalk fiber had superior properties compared to boards made with a mixture of hardwood fibers.