We analyse the method of direct quantization suggested in reference [1] for adamped harmonic osillator, in which the quantum condition xp-px=ihe(-(C/M)t) is introduced. It is pointed out that this method can not be generalized to treat the case in which C is a function of time. In order to treat this case in a general approach, Heiaenberg relation xp-px=in must be kept and the force acting upon the osillatormust be supposed to contain a component fR that does not commute with x and satisfies xfR-fRx=ih(C/M).An electronic osillator is analysed as an example to show that ourapproach is consistent with quantum mechanical Langevin theory.