In this paper an RC time constant digital-tuning method is proposed for multi-bit continuous-time Delta-Sigma modulators. In this approach the effects of the imprecise RC time constant are compensated in digital domain without any requirement to the conventional analog tuning circuitries. In this method, acquiring the response of the loop-filter of the modulator to a known input signal, the actual loop-gain of the modulator is estimated. Comparing the actual loop-gain and the ideal loop-gain, a proper digital IIR (impulse invariant response) filter is inserted in the feedback path of the modulator. Analytic formulas and MATLAB simulations prove that the proposed method compensates the detrimental effects of the imprecise RC time constant appropriately.