Laboratory and screenhouse experiment were conducted to assess the symbiotic effectiveness (SE) of rhizobia isolated from southern Guinea savanna, northern Guinea savanna and Sudan savanna of Nigeria and response of promiscuous soybean varieties, TGx1448-2E, TGx1835-10E and TGx1955-10E to inoculation with ten indigenous rhizobia isolates. The soybean varieties were grown on sterilized sand at the screenhouse of the Department of Soil Science and Land Management, Federal University of Technology Minna and watered using Sandsman’s nutrient solution. The treatments were un-inoculated control, mineral nitrogen (urea) and ten rhizobia isolates arranged on a Completely Randomized Design (CRD) and replicated three times. The rhizobia isolates were Sg4, Sg6-3, Gw5, Gw3-2, Bg3, Bg1-4, Sk2-3, Am2, Am6-3 and Kr5-5 isolated from Sabon-gida, Gwada, Birnin-gwari, Shika, Amawa and Karaye sites of Nigerian savanna. The results obtained were subjected to Analysis of Variance using statistical analysis system (SAS 2008) computer software. The treatments mean was separated using Least Significant Different (LSD) at 5% probability. Nodulation and biomass yield of the varieties were assessed at six weeks after planting. Nodules were only produced in inoculated plants, SE was calculated. The result obtained showed that nodule dry weight, SE and shoot dry weight were significantly affected by the interaction between inoculation and promiscuous soybean varieties. Generally, inoculated plants gave higher shoot biomass gain than the un-inoculated control but lower than those treated with urea. The difference between those inoculated and those treated with urea was associated to environmental specificities and higher temperature during the period of the experiment. The SE was highest in northern Guinea savanna isolate reaching 67% and lowest in southern Guinea savanna isolate Sg6-3 recorded 53%. The result showed an SE of less than 100% in all the isolates which implies that the indigenous rhizobia isolates were not superior to the mineral nitrogen.