Plenty of molecular circuits with specific functions have been developed; however, logic units with reconfigurability, which could simplify the circuits and speed up the information process, are rarely reported. In this work, we designed a novel reconfigurable logic unit based on a DNA‐templated, potassium‐concentration‐dependent, supramolecular assembly, which could respond to the input stimuli of H+ and K+. By inputting different concentrations of K+, the logic unit could implement three significant functions, including a half adder, a half subtractor, and a 2‐to‐4 decoder. Considering its reconfigurable ability and good performance, the novel prototypes developed here may serve as a promising proof of principle in molecular computers.