Abstract: Lentil is one of the most important legume crops in the world, especially in developing countries. In Egypt, root rot and wilt are the most important fungal diseases. Greenhouse and field experiments were conducted to study the effect of Molybdenum (Mo) or Cobalt (Co) on lentil pathogens (Rhizoctonia solani and Fusarium oxysporum) and nitrogen fixation compared with fungicide Rizolex T50. Lentil seeds (cvs. Giza 4 and Giza 9) were soaked 8 h in Mo or Co at concentration of 2 and 5 ppm before seeding while Rizolex T50 was used as seed-coating at 3 g kg-1 seeds. A split plot design with three replicates was used under greenhouse conditions. Results showed that damping off significantly increased in Giza 9 compared to Giza 4. While both Mo and Co decreased it in both cultivars; low level (2 ppm) was more effective. In the field, Mo and Co treatments showed significant decrease in pre and post-emergence damping off as well as dead plants (resulted from root rot and wilt). Additionally, plant height of lentil varieties showed significant increase by Mo (2 ppm) and Co (2 ppm) treatments. Different concentrations of Mo and Co were found to induce high root nodules, nitrogenase activity and nitrogen fixing bacteria. Seed yield increased significantly by Mo and Co treatments except Mo (5 ppm) on Giza 4 variety in second season. Soaking lentil seeds in Mo or Co at 2 ppm is recommended to be incorporated into the production program of lentil to decrease root rot and wilt diseases as well as improve growth and productivity.