The objective of this study was to investigate the effect of inner rod tilting on the transfer function of a cylindrical differential electrical mobility classifier (DEMC), a key component in differential mobility sizers. Applying numerical modeling, we found that the inner rod tilt caused variations in the flow and electrical fields in the DEMC classification channel, consequently deteriorating the DEMC transfer function (i.e., reducing the peak and widening the width). In high-tilt cases, the single peak of the transfer function was split into two. Further investigation revealed that the alternation of the electrical field in the classification channel (due to rod tilting) was primarily responsible for this deterioration, which was particularly pronounced for a high sheath-to-aerosol flow ratio. However, increasing the total DEMC flow reduced the adverse effects of rod tilting on the transfer function. Finally, increasing both the radii ratio, R2/R1 (the outer cylinder radius to the inner rod radius), and the classification channel length, L, negatively impacted the transfer function.