The study was conducted at the experimental field of the Department of Environmental Science, Bangladesh Agricultural University, Mymensingh (24' 27" N, 90,50" E, elevation 18 m) to determine the fundamental process and trend of radiation interception and biomass production by rainfed rice. Radiation interception varied in various stages of rice growth in relation with leaf area index (LAI) and light extinction coefficient (k). Higher radiation interception was observed at 276 days of the year (DOY) when LAI was 5.24 and k value was 0.35. Linear relationship was found between cumulative total dry matter and cumulative intercepted photosynthetically active radiation. The mean radiation use efficiency (RUE) was 2.54.