The two-layer MoSi2/MoB composite coatings were developed using the halide activated pack cementation (HAPC) method on Mo substrate. Oxidation resistance property and microstructural evolution of the coatings at high temperatures were investigated. During oxidation exposure, the coatings exhibited a good oxidation resistance property. The mass gains of the coated specimens oxidized at 1200°C for 100h and at 1300°C for 80h were 0.270 and 0.499mg/cm2, respectively. Compared with the monolithic MoSi2 coatings, the transformation of MoSi2 phase in the MoSi2/MoB composite coatings was more sluggish at elevated temperatures. The growth rate constant of the Mo5Si3 layer in the composite coatings was two orders of magnitude lower than that of the Mo5Si3 layer in the monolithic coatings at 1300°C. The microstructural degradation of MoSi2 in the composite coatings at high temperatures was slowed by the introduced MoB layer. The MoB layer in the composite coatings is useful to prolong the service life of MoSi2 coatings at high temperatures. •MoSi2/MoB composite coatings was developed using the in-situ CVD.•MoSi2/MoB composite coatings exhibited a good oxidation resistance property.•The microstructural degradation of MoSi2 in the composite coatings was sluggish.•The Mo5Si3 layer in the composite coatings developed slowly.