Alfalfa weevil, Hypera postica Gyllenhal, is regarded as one of the most important insect pests on Chinese milk vetch and hairy vetch. The insect usually feed on leaves, stems and pods of the green manure which causes severe reduction of biomass. This study was conducted to observe the occurrence of H. postica larva and adult on Chinese milk vetch in 2009 to 2010, and to evaluate host plants preference of 11 different seedlings in 2010, Milyang, Korea. Occurrence of H. postica larvae on Chinese milk vetch was observed to increase from early April clearly and its peak population was showed during middle to late April. The 1st generation of newly emerged adult of H. postica was appeared on 20th May. Newly emerged H. postica adult was fed on green manure such as Chinese milk vetch and hairy vetch as well as various seedlings located at nearby upland. And then the insects were migrated into aestivating places in middle to late of June. Thus, host plant preference of H. postica adults were evaluated with 11 different seedlings using transparent acrylcage and at Chinese milk vetch field. As a result, H. postica adult preferred on Chinese cabbage, followed by soybean, kale, foxtail millet and proso millet. The damaged rating of seedlings were shown to have the same trend with adult occurrence. In particular, few H. postica adults were occurred on eggplant, lettuce, corn, crown daisy and peanut, and thereby those crops were regarded as non-preference plants due to the absence of damage. These informations can be used by upland farmers who sowing from late May to early June for effective management of H. postica.