The secondary electron emission properties of rare-earth-doped molybdenum emitter made by aqueous solution-solid doping method, its microstructure and surface behavior are discussed in this paper. The experimental results show that adding rare-earth oxides La2O3,Y2O3 and Gd2O3 into molybdenum raises the maximum secondary electron yield dm from 1.25 of clean Mo to 2.0-3.24 of doped molybdenum when heated to 1100-1600 8C in vacuum. With increasing percentage content of doped rare-earth oxide dm is enhanced in some extent. dm remains nearly constant during 1000h of test period when cathodes are operated at 1100 8C and under primary electron bombardment with bombarding energy of 1000 eVand bombarding power of 300W/cm2. This demonstrates such cathodes have good anti-bombing insensitivity. A work function of about 2.7-2.8 eV is obtained from Richardson lines. SEM observations and EDS analysis show that distribution of rare-earth oxides in the cathode body is inhomogeneous and tends to aggregate at molybdenum grain boundaries. By AES analysis it is found, that atomic concentrations of La and Yon the surface are about 2.5 times higher than in the bulk for a sintered body and further increase after activation.We believe the rare-earth atoms segregated at the grain boundaries diffuse along the grain boundary during the process of cathode activation. Therefore, the surface of the cathode is covered by a certain amount of rare-earth oxide. As a result, the secondary electron yield is improved.