Mexican yam plant (Pachyrhizus erosus (L.) Urban) is a new and hence less-known crop plant in Iran, with potential applicationes in food and pest control industries. Therefore, the present study was conducted to determine the best fertilizer treatments and its effect on the morphological characteristics and grain yield of Mexican yam bean plant in a semi-arid region. The experiment was carried out as a randomized complete block design with six replications in Kazeron, Fars province, south of Iran. The treatments included the control, EM biofertilizer (40 L/ha), Vinas organic fertilizer (80 L/ha), and the combination of bio-organic fertilizer (the optimum level of fertilizer was determined based on the results of previous experiments). Fertilizer treatments had a significant effect (at 1% probability level) on plant height, plant fresh and dry weight, pods/plant, grains/pod, stem diameter, grain and biological yield and harvest index, photosynthetic pigments concentration and grain protein content. The mean comparison showed that in the combined treatment of Vinas organic fertilizer and EM, the fresh and dry weight of the plant (67.6 grams and 26.8 g, respectively), the height of the plant (56.1 cm), grains/pod (6.4), pods/plant (6.3), biological yield (4929 kg/ha), grain yield (527 kg/ha), harvest index (10.7%), concentration of chlorophyll a, b, and total chlorophyll and carotenoid concentration (9.83, 3.43, 13.5 and 3.28 mg/g fresh weight, respectively), grain protein (34.1%) were more than control. Also, the stem diameter showed the greatest increase compared to the control. The results suggested the superiority of the bio-organic fertilizer treatment at the optimal level (40 and 80 L/ha) and the positive response of Mexican yam bean plant to these fertilizers.