Nitrogen is an essential element in the growth and reproduction of plants whose deficiency in the soil is often the limiting factor in crop production. To compensate for the lack of nitrogen, very often the advantages of beneficial associations between rhizobia and legumes are utilized. Symbiotic nitrogen fixation has a unique role in the entry of nitrogen into the soil presenting an important component in achieving higher yields of different legume crops. It is important to select highly efficient rhizobial strains adapted to different soil conditions. Alfalfa (Medicago sativa L.) is a very important forage crop, which forms a symbiotic relationship with nodule bacteria Sinorhizobum meliloti. In order to increase the yield of this forage crop, the inoculation of alfalfa with high quality rhizobial strains is recommended. The main aim of this study was to select indigenous S. meliloti strains, isolated from different regions of Croatia, to adverse environmental conditions. The growth of the strains was studied at different pH values, temperatures, carbohydrate sources and different concentrations of NaCl. The sensitivity of strains to different antibiotics was tested and growth curve was formed for each isolate. Biochemical tests were used for determination of the biochemical characteristics of strains: catalase test, urease test and lactose agar test. The results showed that most of the strains can grow at temperatures higher than optimal and that strains tolerate the both acidic and alkaline environment. It was found that the strains grow at lower (1%, 2%) concentrations of NaCl, while they do not tolerate high (3%, 4%) concentration of NaCl. Lactose agar assay indicate that three strains probably belong to the genus Agrobacterium. Most strains possess the enzyme urease while only a small number of them possess the enzyme catalase. The results showed that all indigenous strains belong to the group of fast-growing rhizobia. In most cases, the sensitivity of indigenous strains to applied antibiotics was determined. The overall results suggest that indigenous S. meliloti strains are more tolerant to adverse soil conditions in relation to the reference strain S. meliloti 2011. High tolerance to unfavorable environmental conditions was determined for indigenous strains I1,I5, NG1 and Z3 and therefore, these strains could be included in further selection programs.