The mobile ad hoc network (MANET) has attracted lots of attention recently. Most of the researches assume that every mobile host in the MANET uses a fixed data rate and follows a distributed coordination function (DCF) to transmit messages. As we know that none of the research has combined multiple data rates and transmission scheduling to minimize waiting time and conserve energy for a MANET with power-saving (PS) mode hosts. IEEE 802.11 has already supported multiple data transmission rate. However, how to decide the transmission rate is still an open question. Here, we propose a data rate selection protocol to select the best available data rate to transmit messages. After the data transmission rate has been selected, we can schedule each transmission according to the data transmission rate and the packet size. Our goal is to minimize the average waiting time of each transmission and thus the PS hosts can switch back to power-saving mode as soon as possible. Therefore, we follow the shortest job first policy to let the transmission with shortest transmission time to access the channel first. Simulation results show that our scheduling protocol can achieve high packet delivery rate, reduce waiting time and conserve lots of energy.