Aims:To study the effect of different nitrogen fertilizer rates on growth, carbon assimilation and biochemical changes of Polygonum minus. Study Design: Polygonum minus were treated with different nitrogen fertilizer (0 kg N ha -1 , 50 kg N ha -1 , 100 kg N ha -1 and 150 kg N ha -1 ) using Urea (46%N) as a source of nitrogen. This experiment was arranged in Randomized Complete Block Design (RCBD) with three replications. Place and Duration of Study: The experiment was conducted at Taman Pertanian Universiti (TPU), Universiti Putra Malaysia between April 2017 to July 2017. Methodology: The growth parameters measured includes the leaf number, plant height, diameter of the stem, and the leaf area. The carbon assimilation parameters were measured using LICOR 6400XT Portable Photosynthesis System. Total phenolic and flavonoids contents from the leaves extracts of Polygonum minus were measured using Folin-Ciocalteu reagents.