Therapeutic enzymes hold great promise for cancer therapy; however, in vivo remote control of enzymatic activity to improve their therapeutic specificity remains challenging. This study reports the development of an organic semiconducting pro-nanoenzyme (OSPE) with a photoactivatable feature for metastasis-inhibited cancer therapy. Upon near-infrared (NIR) light irradiation, this pro-nanoenzyme not only generates cytotoxic singlet oxygen (1O2) for photodynamic therapy (PDT), but also triggers a spontaneous cascade reaction to induce the degradation of ribonucleic acid (RNA) specifically in tumor microenvironment. More importantly, OSPE-mediated RNA degradation is found to downregulate the expression of metastasis-related proteins, contributing to the inhibition of metastasis after treatment. Such a photoactivated and cancer-specific synergistic therapeutic action of OSPE enables complete inhibition of tumor growth and lung metastasis in mouse xenograft model, which is not possible for the counterpart PDT nanoagent. Thus, our study proposes a phototherapeutic-proenzyme approach toward complete-remission cancer therapy.