A study on effect of long term use of fertilizers on weed dynamics in maize – wheat cropping system was conducted at Birsa Agricultural University, Ranchi during 2013 to 2016 The treatments included three levels of N 40, 80 and 120 kg ha-1, P2O5 0, 40 and 80 kg ha-1 and two levels of K2O, 0 and 40 kg ha-1 each for maize and wheat in fixed plots. The treatment absolute control N0P0K0 was also included in the treatments. The experiment was conducted under confounded design with three replications. Minimum weed population and dry matter accumulation was recorded in maize during all the years under absolute control (N0P0K0). As the levels of nitrogen, phosphorus and potash increased, the weed population and dry matter accumulation also decreased. The interaction of N, P and K revealed that with increasing combination of N and P, weed dry matter accumulation increased upto 40 kg P ha-1 and it reduced at 80 kg P ha-1. With increase of N and K level the weed dry matter reduced. The maize grain yield continued to increase up to highest level of nutrient applied. In case of wheat, as the level of P and K combinations increased, the grain and weed dry matter accumulation also increased. Combination of P with 40 or 80 kg N ha- 1 without K increased weed dry matter accumulation as well as wheat grain yield, while, weed dry matter accumulation reduced with addition of 40kg K ha-1 with N and P irrespective of their levels. Wheat yield increased with reduced weed dry matter