The magnetic properties and magnetocaloric effects of Mn5Ge2.7M0.3(M=Ga, Al, Sn) compounds have been studied. All samples crystallize in the hexagonal Mn5Si3-type structure with space group P63/mcm. The average Mn magnetic moment decreases and the Curie temperature remains almost unchanged by the substitution of M for Ge. The magnetic entropy changes in these compounds are determined from the temperature and field dependence of the magnetization using the thermodynamic Maxwell relation. The substitution of M for Ge reduces the magnitude of the magnetic entropy change owing to the decrease of the magnetic moment but broadens the magnetic entropy change peak. The maximum magnetic entropy changes for a field changes of 4.0×106A·m-1 are 6.1, 6.3, and 5.3J·kg-1K-1 for M=Ga, Al, and Sn, respectively. In addition, anomalies are found in the Arrott curves of Mn5Ge2.7M0.3(M=Ga Al, Sn) compounds under a critical field Hc when the temperature is higher than the Curie temperature TC, which indicates that the paramagnetic susceptibilities of these compounds change sharply. The value of Hc increases almost linearly with increasing temperature. This phenomenon is probably due to the change of Fermi energy by the applied magnetic field, which reduces the number of the effective charges.