Grass pea (Lathyrus sativus) is the most widely distributed and the third most important pulserncrop in Ethiopia. It grows in a wide range of altitudes and survives in scarce moist conditions andrnfixes nitrogen with rhizobia and performs well in less fertility soils. However, the effectiveness inrnnitrogen fixation varies depending upon the host varieties, type of strain and differentrnenvironmental characters. It is, therefore, necessary to evaluate the efficiency of different isolatesrnfrom different sampling areas. Thus, 68 grass pea rhizobial isolates (47 from South Wollo and 21rnfrom West Shoa) were isolated and characterized on the basis of different characters. Thesernisolates were reinoculated on pouch culture using â€œWasseâ€ variety of grass pea to authenticaternnodulation and determine their symbiotic effectiveness. All but 5 isolates were authenticated asrnroot nodule bacteria with their capacity to infect and nodulate their parent host. Most of thernisolates displayed fast doubling time (1.2-4hrs) and large colonies (2-6.0 mm) and changed thernBTB-YEMA media to yellow which showed that they are fast growing rhizobia and thenrncategorized into R. leguminosarum bv. viceae. The preliminary screening of the isolates forrnsymbiotic effectiveness on pouch culture showed that isolates AAUGR (31, 37, 41 and 47) ofrnSouth Wollo and AAUGR (48, 49, 52, 59, 60, 61, 66 and 67) of West Shoa that comprised ofrn19% of the isolates were highly effective whereas, 43% were found to be effective. Three highlyrneffective isolates from South Wollo (AAUGR 31, AAUGR 37, and AAUGR 41) and four highlyrneffective isolates from West Shoa (AAUGR 48, AAUGR 59, AAUGR 61, and AAUGR 67) werernreinoculated into soil culture to evaluate their performance in the natural environment (soil). Allrnthe selected isolates were found to accumulate 112-149 % of SDM that was higher than therncontrols. Isolate AAUGR 37 (SW) accumulated the highest SDM of all the inoculated treatmentsrnand the controls. All the selected isolates were found to perform better on pot culture than onrnpouch culture. Almost all of the isolates were able to grow at extremely low and high pH, low andrnhigh salt, low and high temperature, and utilized a wide range of carbohydrate and nitrogenrnsources and displayed high resistance to several antibiotics indicating that the isolates canrncompete in their natural environment. The result of the numerical analysis also showed thernexistence of diversity among the tested isolates.