Cropping patterns that increses crop yield and land use efficiency through intercropping are becoming increasingly popular worldwide, especially in developing countries. Despite many advantages related to nutrient, light, temperature, water, and land use efficiencies, intercropping of rice subspecies such as Indica and Japonica has not been exploited yet. Hence, a two-year field experiment was conducted to study the effects of Indica-Japonica (i.e., XLY900-YY9 and YLY900-YY9) intercropping on the rice yield depending on sowing dates, and the intercropping effects were evaluated by yield, land equivalent ratio (LER), interspecific competitiveness (A), and relative crowding index (K). The Indica-Japonica intercropping had cumulative yields of 12 t ha ^–1 (20-23 %) higher than the yield of Indica or Japonica under mono-cropping, which was mainly due to the increase in photosynthetic rate that come through the efficient utilization of light. The LER and relative crowding index (K) of Indica-Japonica under intercropping systems were > 1, suggesting intercropping was more advantageous and efficiently utilized the land. The interspecific relative competitiveness (A) of Indica and Japonica was greater than 0, indicating reduced competition between the companion crops for availiable light and space resources. Hence, Indica-Japonica intercropping has high potential to maximize rice yield while utilizing the natural resources more efficiently, and could contribute to food security, particularly in regions where rice is a staple crop.