With reduced background and high sensitivity, photoelectrochemistry (PEC) may be applied as an intracellular nanotool and open a new technological direction of single‐cell study. Nevertheless, the present palette of single‐cell tools lacks such a PEC‐oriented solution. Here a dual‐functional photocathodic single‐cell nanotool capable of direct electroosmotic intracellular drug delivery and evaluation of oxidative stress is devised by engineering a target‐specific organic molecule/NiO/Ni film at the tip of a nanopipette. Specifically, the organic molecule probe serves simultaneously as the biorecognition element and sensitizer to synergize with p‐type NiO. Upon intracellular delivery at picoliter level, the oxidative stress effect will cause structural change of the organic probe, switching its optical absorption and altering the cathodic response. This work has revealed the potential of PEC single‐cell nanotool and extended the boundary of current single‐cell electroanalysis. An integrated photocathodic nanotool was fabricated for dual‐functional intracellular drug delivery and evaluation of cellular oxidative stress in single live cell.