This study involved the application of natural materials to produce interlocking blocks for thermal conductivity and sound absorption by mixing rice straw and rice husk ash. The ratios of soil, cement and sand used in the mix was 5:1:1. The mixing ratios of rice straw were zero, 1, 2 and 3% and those of rice husk ash were 10, 20 and 30% of the weight of cement. The test included the measure of compressive strength, unit weight, water absorption, porosity, thermal conductivity and sound absorption using blocks at the age of 28 days. The results showed that the addition of rice straw caused the compressive strength to reduce, while porosity and water absorption were increased. The addition of rice husk ash helps to improve the compressive strength and unit weight. All of these qualities passed the Thai Industrial Standard TIS 58-2533 (TIS 1990). The increasing of rice straw and rice husk ash resulted in low thermal conductivity and better sound absorption. Therefore, rice straw and rice husk ash are interesting materials in the production of energy-saving building materials.