The demand for vegetables in Riau Province remains high, but the current production is insufficient. As a result, vegetables are sourced from other regions, such as West Sumatra and North Sumatra. To address this issue, there is a need to increase vegetable production. The study aimed to investigate the impact of concentrated rice washing water and organic NPK application on the growth and production of caisim mustard greens (Brassica juncea L). The study utilized a completely randomized factorial design with two factors. The first factor was rice washing water, which had four treatment levels: 25%, 50%, 75%, and 100%. The second factor was organic NPK, which had four treatment levels: no organic NPK, 1.5 g/plant, 3.0 g/plant, and 4.5 g/plant. The parameters observed included the number of leaves, wet weight, economic weight, dry weight, net assimilation rate, and relative growth rate. The study's results indicated that the interaction between rice washing water and organic NPK significantly affected all observed parameters. The best treatment was applying 75% rice washing water and 4.5 g organic NPK per plant. The main effect of rice washing water application was also significant on all observed parameters, with the best treatment being 75% rice washing water. Similarly, the main impact of organic NPK was significant on all observed parameters, with the best treatment being 4.5 g per plant.