A mobile ad hoc network (MANET) is one consisting of a set of mobile hosts capable of communicating with each other without the assistance of base stations. One prospective direction to use such networks is to adopt positioning devices (such as global positioning system, GPS) to provide location-aware services. This paper discusses an attractive service called geocasting, or location-based broadcasting, whose goal is to send a message targeted at mobile host resident within a specified geographical region (such as a building, a street, a commercial area, etc.). In this paper, we propose a new routing protocol for geocasting called GeoGRID, which is based on our earlier unicast protocol GRID [14]. The protocol is featured by utilizing location information, confining the flooding zone, and electing a special host in each grid area responsible of forwarding the geocast messages. Simulation results show that our GeoGRID protocol can reduce network traffic and achieve higher data arrival rate.