We propose a novel multicast routing protocol, called adaptive multicast routing protocol for MANETs (Mobile ad hoc routing protocol). Multicast routing protocols can be classified two types according the structure used to establish route. Existing protocols are either tree-based or mesh-based. In mesh-based routing protocols, a reliable protocol ODMRP was proposed. In ODMRP, each sender has to broadcast control packet periodically in order to build mesh. But with an increase of number of senders, control overhead causes reliability reduced because of a large amount of overhead and collisions. Hence, ODMRP is not work well in this case. We proposed our scheme to aim at the drawback of ODMRP. We use packet delivery ratio (PDR) to determine if the load of network is congestion. When packet delivery ratio is high, it means that the network traffic load is low, and vice versa. We determine whether a sender broadcasts Join-Query control packet or not according to packet delivery ratio. As packet delivery ratio is decrease, a sender does not broadcast Join-Query as far as it can in order to avoid collisions. However the packet delivery ratio is increase, senders have strong probability to broadcast Join-Query to establish mesh nodes. We can improve reliability and reduce overhead is caused by control packets with this way.