Abstract: This research investigated the effect of Mucaojing (imazethapyr 5%) application time on the productivity of alfalfa on the Shandong peninsula. Plant height, biomass, crude protein (CP) content, acid detergent fiber (ADF) and neutral detergent fiber (NDF) were assessed after application of Mucaojingat 4 stages. The results showed that Mucaojing application reduced plant height slightly when applied at emergence and seeding stages; biomass significantly increased (P<0.05) when Mucaojing was applied at seeding. Mucaojing did not affect leaf-stem ratio. CP was negatively correlated with application time; when applied at emergence CP content was significant higher (P<0.05) than treatment at the pre-sowing stage. NDF and ADF were significantly reduced (P<0.05), by Mucaojing application. In conclusion, the application of Mucaojing at the emergence stage increased alfalfa biomass and CP content under rain-fed conditions.