A sensor array consisting of a chemically modified sensor in which 4-carboxybenzo-18-crown-6 was immobilized onto a screen-printed carbon nanofiber-modified electrode (crown-6-SPCNFE) and an ex-situ antimony film deposited on a screen-printed carbon nanofiber-modified electrode (ex-situ-SbSPCNFE) was applied for the resolution of the strong overlapped signals resulting from the simultaneous determination of Tl(I) and In(III) by stripping voltammetry. A Partial Least Squares model was constructed and good calibration curves of predicted vs. expected concentrations of the considered metal ions, with correlation coefficients higher than 0.98 for both training and test sets, were obtained. These results provided by the sensor array were compared with those obtained by a single electrode. Moreover, this sensor array was successfully applied for the voltammetric determination of both Tl(I) and In(III) in tap water, providing comparable results to those obtained by ICP-MS measurements.