This work was conducted to determine the effect of inoculation with biofertilizers (mixture of Azotobacter chroococcum, Azosphillum lipoteerum, Bacillus polymixa, Elaallus rnegatherium and Pseuobmonas fluorescence) and two levels of chemical fertilizers NPK (nitrogen, phosphorous and potassium) at the ratio of 1 : 1 : 1 at the rate of 3 or 6 gm/plant/20 an plastic pot on the main constituents of cosmos plants. Application of NPK at the rate of 3 g plant/20 an plastic pot increased N content in flowers and K content in the herb, while the rate of 6 g/plant increased the carbohydrates percentage in both herb and flowers. The highest content of chlorophyll (a) and carotenoids in leaves and P in herb were found in the plants inoculated with the biofertilizers and received NPK at 6 g/plant Meanwhile, the combined inoculation of biofertilizers and NPK at 3 g/plant resulted in the highest content of K in flowers. The highest content of chlorophyll (b) in leaves and P content in flowers resulted from inoculating the plants with the biofertilizers as well as applying them to the plants as drench plus application of NPK at 3 g/plant, however increasing the rate of NPK to 6 g/plant instead of 3 g/plant led to an increment in N content in the herb.