Abstract: The K-shell x-ray emission rates of molecules have been calculated with the DV-X α method. The x-ray transition probabilites are evaluated in the dipole approximation by the DV-integration method using molecular wave functions. The validity of the DV-integration method is tested. The calculated values in the relaxed-orbital approximation are compared with those of the frozen-orbital approximation and the transition-state method. The contributions from the interatomic transitions are estimated. The chemical effect on the Kβ/Kα ratios for 3d elements is calculated and compared with the experimental data. The excitation mode dependence on the Kβ/Kα ratios for 3d elements is discussed.