The most common legume in Northern Kazakhstan is sainfoin. Sainfoin has the unique ability to enter into symbiosis with rhizobia, forming nitrogen-fixing nodules which have the ability to absorb 125-480 kg/ha of nitrogen from the air annually. These high yields of cheap vegetable protein are achieved without the use of mineral fertilizers. However, in the arid steppes of northern Kazakhstan root system nodules are not formed due to the moisture deficit in the soil. The objective of the current research is to identify new and promising varieties and sainfoin lines with high nitrogen-fixing ability. To increase the nitrogen-fixing capacity of promising new sainfoin lines, plant seeds were inoculated before sowing with an experimental biopreparation based on nodule bacteria (nitragin) obtained in microbiology laboratories from the local strains of rhizobia to Sainfoin Rhizobium simplex (Rs.–5 is for the sainfoin). These studies showed that new lines seeds inoculated with rhizobia promotes more active nitrogen fixation compared to the plants not treated with nitragin. Using the chromatographic method of determination of the nitrogen-fixing ability in new Sainfoin lines K-185 and K-209 it was found that during the growing season fixed nitrogen balance in the atmosphere was respectively 491 and 458.7 mg/ha of the total nitrogen balance of 84 %. This shows that new Sainfoin lines have a more active ability to fix atmospheric nitrogen after inoculation rhizobia than the standard variety of sainfoin. Sainfoin lines K-209 and K-185 proved to be the best forms of sainfoin for nitrogen-fixing conditions in Northern Kazakhstan