This paper presents a new respiratory impedance esti- mator to minimize the error due to breathing. Its practical reliability was evaluated in a simulation using realistic signals. These signals were generated by superposing pressure and flow records obtained in two conditions: 1) when applying forced oscillation to a resistance-inert- ance-elastance (RIE) mechanical model; 2) when healthy subjects breathed through the unexcited forced oscillation generator. Imped- ances computed (4-32 Hz) from the simulated signals with the new es- timator resulted in a mean value which was scarcely biased by the added breathing (errors less than 1 percent in the mean R, I, and E) and had a small variability (coefficients of variation of R, I, and E of 1.3, 3.5, and 9.6 percent, respectively). Our results suggest that the proposed estimator reduces the error in measurement of respiratory impedance without appreciable extracomputational cost.