Alfalfa is one of the main crops ensuring the creation of fodder base and increasing the share of vegetable protein. It also accumulates biological nitrogen in the soil, contributes to the accumulation of humus in the soil, prevents the soil erosion, contributes to soil structure, restores its formation and improves the ecological situation in agriculture. If American specialists argue that alfalfa is the green gold of the Great Plains, then our specialists said that "it is the green gold of Moldavian cernozems” [1, 2]. With all the good qualities that this culture have, in the last few decades for various reasons it has not been given attention, which led to its loss of productivity. In order to stabilize and increase plant productivity, an important role is played by the development of new intensive technologies of alfalfa cultivation using microbial fertilizers, growth stimulators, varieties with increased protein yield, also being used in optimal doses mineral and organic fertilizers. Given, however, the fact that fertilizers are quite expensive, it is necessary to seek another remedy for plant nutrition. This remedy can be obtained from the rhizosphere and rhizoplane of alfalfa plants (3, 4, 5). Based on the above mentioned, our collective undertake field trips in various pedo-climatic areas of the country where alfalfa plants were collected and there were isolated, in laboratory conditions, 20 strains of bacteria Rhizobium meliloti – symbiotroph nitrogen fixing in alfalfa. After the purification procedure, they were studied in laboratory conditions, finally being selected the following strains of Rhizobium meliloti: 2/13, 3A, RS-B2, RP2, 29/30, 833 etc. Thus, the parameters of capacity of biomass storage and of virulence in nominated bacteria were studied. It was established that bacterization of alfalfa seeds stimulates the accumulation of green mass, it increased by 30.7% compared to the control and of dry mass – by 36.6%. The number of nodules formed on the roots of the plants has increased from 7.3 to 29.4%. In field conditions, on small plots, in 2014, there were investigated four strains of bacteria Rhizobium meliloti 19K, RS-B2, RP2, RDm1 with the aim of assessing their effect on the productivity of alfalfa variety Tuna. Plant harvesting occurred in bud-flowering phases. After the analysis of data obtained, it was found that green mass increased by 5.0 to 32.5% compared to the control. In this regard, the bacterium Rhizobium meliloti RS-B2 was highlighted.  As a result of investigations, the following conclusions were made: • Soil and plant samples contained multiple strains of Rhizobium meliloti nodule bacteria; • In laboratory experimental conditions were highlighted the following strains of Rhizobium meliloti: 3A, 2/13, 29/30, RP2, RS-B2 with increased activity in alfalfa biomass accumulation and under field conditions, Rhizobium meliloti strain RS-B2 was more pronounced.