The System of Rice Intensification (SRI) has been spread very quickly in southern Cambodia. To understand the motivation of farmers in adapting SRI, and its benefits, we conducted an onfarm study at Popel commune, Tramkak district, Takeo province in southern Cambodia, during the 2012 and 2013 wet season. We noticed a significant difference between SRI and conventional farmers’ practices (FP) in rainfed lowland rice ecosystem. Despite of low nitrogen input, without chemical fertilizers, high grain yield was achieved in SRI 1 (6.0 t ha) and SRI2-Bottom (7.2 t ha-1) in 2013. SRI 1 and SRI 2 of panicle and number of panicle were high than SR 3, FP 2, and FP 3 due to early transplant. Relationships between total number of spikelet and plant nitrogen were (r2 = 0.95) highly positive at harvest. SRI fields were, most of them achieving highly superior yield and number of panicle compared to their FP fields. The results indicated that SRI practices of planting younger seedling, with organic material and topography of paddy, lead to increased grain yield.