Abstract: Adopting the method of foliar application, the experiment was conducted to investigate the effect of Mn and B on herbage yield and quality of alfalfa. The results showed that foliar application of Mn and B could increase the herbage yield of alfalfa. Among the 3 rates, the Mn 200mg/kg（Mn2）and B 600mg/kg (B3) were the most effective and suitable application rates, remarkably (P 0.05) increasing the herbage yield by 809.49 and 1065.35 kg/hm2 respectively, as compared with CK. Spraying Mn could significantly (P 0.05) increase Zn and Mn content of alfalfa, and the appropriate spraying could significantly (P 0.05) increase P, Co, Se, Fe and Mo content; while spraying Mn could reduce Ca, Cu and B content of alfalfa, and the appropriate spraying could significantly (P 0.05) reduce Ca and Cu content. Mn content of alfalfa increased with the increasing application of Mn fertilizer, Se and Cu content decreased with the increasing application of Mn fertilizer, Fe and Zn content increased first and then decreased with the increasing application of Mn fertilizer. Spraying B could significantly (P 0.05) increase P and Zn content of alfalfa, and reduce Ca, Mo and Se content, and the appropriate spraying of B could significantly (P 0.05) increase Co, Fe, Mn and B content; However Spraying B could not remarkably(P 0.05) reduce Cu content of alfalfa. Zn and B content of alfalfa increased with the increasing application of B fertilizer, Fe, Ca, Se, Mo and Cu content decreased with the increasing application of B fertilizer, Mn and P content increased first and then decreased with the increasing application of B fertilizer.