A novel enzyme-free photoelectrochemical (PEC) immunoassay was developed for the ultrasensitive detection of prostate specific antigen (PSA) based on the DNA-mediated nanoscale zirconium-porphyrin MOFs (NMOFs). By virtue of the intrinsic coordination between unsaturated zirconium sites of the NMOFs frameworks and phosphonate groups, the 5′-phosphorylared ss-DNA-tagged antibody (Ab-DNA) conjugate with a consecutive stretch of guanines as a spacer could be loaded on the NMOFs easily, obtaining a novel type of Ab-DNA-functionalized NMOFs complex. Additionally, as a photocathode PEC active nanomaterial, NMOFs exhibited a significant enhanced photocurrent response with the presence of dopamine under oxygen-containing aqueous media at −0.3 V (vs Ag/AgCl). Furthermore, with the aid of the electrochemical grafting of polyamidoamine (PAMAM) dendrimers functionalized interface, the novel type of Ab-DNA–NMOFs further served as a PEC signal nanoprobe for the ultrasensitive PSA immunoassay. Under optimal conditions, the corresponding immunosensor possessed a wide calibration range of 1 pg mL^–1 to 10 ng mL^–1 and a limit of detection (LOD) of 0.2 pg mL^–1. This present work demonstrated the promising application of DNA-mediated NMOFs in developing highly sensitive, environmentally friendly, and cost-effective PEC biosensors.