Peppermint is one of the most important medicinal plants that widely used in food, cosmetics and drug industries. In this investigation, the effects of biofertilizers (Nitroxine and Thiobacillus) on morphological and phytochemical properties of Mentha pipertita L. studied. An experiment including 16 treatments and 3 replications was conducted according to a completely randomized blocks in a factorial arrangement in the research field of University of Zanjan. The treatments were consisted of Nitroxine (0, 2, 4, 6 l/ha), and Thiobacillus (0, 4, 6, 8 kg/ha) incorporated with sulphur (300 kg/ha). The evaluated traits were including yield and yield parameters (fresh weight, dry weight, essential oil percent, stem length, shoot numbers, chlorophyll content, leaf length, leaf width, inflorescence numbers, inflorescence length, stem diameter, leaf relative density, leaf area index, Secretory glands, node numbers and internode length). The results showed that maximum leaf area, leaf length, leaf width, shoot numbers, number of Secretory glands and essential oils content in combination of 6 kg/ha Thiobacillus and 6 l/ha Nitroxine. Also the highest stem length and internode length was observed in 4 kg/ha Thiobacillus and 2 l/ha Nitroxine. The maximum number of inflorescence was recorded in 4 l/ha Nitroxine. However, the maximum inflorescence height was observed in 4 kg/ha Thiobacillus in combination with 6 l/ha Nitroxine. In conclusion, the combination of 6 kg/ha Thiobacillus and 6 l/ha Nitroxine can be recommended to obtain maximum yield and essential oils in this medicinal plant.