This study aimed to determine the effect of rice straw compost and rice husk ash on some chemical properties of an Ultisol soil under sweet corn plant. This study was conducted at the Labuhan Batu Rantau Prapat University Campus Land and at the PT. Socfindo Laboratory. The design used in this study was a factorial randomized design consisting of two factors with two replications. The first factor was application of rice husk ash with four dose levels (g 5 kg-1 of soil), ie P0 (0), P1 (10), P2 (20), and P3 (30). The second factor was the application of rice straw compost with four dose levels (g 5 kg-1 of soil), ie J0 (0), J1 (25), and J2 (50), J3 (75). Results of this study indicated that the application of rice straw compost significantly increased soil organic-C and available P contents, as well as plant height, plant dry weight, N and P uptake by plant. The treatments, however, did not significantly increase soil pH and total-N content. The application of rice husk ash significantly increased soil organic-C content and N uptake by plant, but it did not significantly increase pH, available P content, and total N content of the soil.