Certain lapwing species (Vanellus spp.) breed in agricultural habitats, where they are dependent on particular features of such artificial conditions. The breeding behavior and breeding success of the Grey-headed Lapwing Vanellus cinereus were examined on farmland in central Japan. Thirty-five pairs in 2004 and 42 pairs in 2005 were observed nesting on farmland consisting mainly of rice fields. Nests appeared to be distributed such that aggregations seemed to function as semi-colonies. Farming practices seriously affected breeding success: 33 (42.9%) breeding attempts were prevented during farming cultivation and flooding in spring. In 2004, only 16 (45.7%) pairs produced fledglings, and in 2005 only 14 (33.3%) pairs were successful. Territory size was also a factor affecting breeding success; territory area was positively correlated with the number of fledglings produced per nest. Grey-headed Lapwing parents intensively defended their nests and chicks; furthermore, group defense by multiple adults was also observed frequently. Defensive behavior was mainly directed against avian predators such as crows (Corvus spp.) and raptors, with group defense more frequently against raptors. Group defense was also more likely to occur where nests were close together, and it seemed that such defense was effective in increasing the number of chicks hatched. The breeding success of Grey-headed Lapwing was found to be influenced both by environmental and behavioral factors.