BACKGROUND: Tumor-derived exosomes (TEX) have shown great potential for drug delivery and tumor targeting. Here, we developed a novel multi-drug loaded exosomes nanoprobe for combined antitumor chemotherapy and photodynamic therapy, and monitoring the drug delivery capabilities with pre-targeting technique. METHODS: TEX of human colorectal cancer HCT116 was prepared, and Doxorubicin and the photodynamic therapy agent 5-aminolevulinic acid (ALA) were loaded and named as TEX@DOX@ALA. Tumor uptake was first examined using fluorescence imaging of the fluorescent dye Cy5 (TEX@DOX@ALA@Cy5). Visualization of exosome aggregation in tumor were realized by positron-emission tomography/computed tomography (PET/CT) with pre-targeting technique. Tumor-bearing mice were first injected with TEX@DOX@ALA labeled with azide (N) (TEX@DOX@ALA@N), and then Ga-(2,2'-((6-amino-1-(4,7-bis (carboxymethyl)-1,4,7-triazonan-1-yl) hexan-2-yl) azanediyl) diacetic acid-dibenzocyclooctyne (Ga-L-NETA-DBCO) was injected after 24 h for PET/CT imaging via in vivo click chemistry. For the antitumor therapy with photodynamic and/or chemotherapy, seven groups of tumor-bearing mice with different therapy were monitored, and the tumor size, animal weight and the survival time were recorded. Furthermore, the samples of blood and interested tissues (heart, lung, liver, kidney, and spleen) were harvested for hematological analysis and H&E staining. RESULTS: The drug loading process did not influence the structure or the function of the HCT116 TEX membranes. In a fluorescence imaging experiment, higher fluorescence could be seen in tumor after TEX@DOX@ALA@Cy5 injected, and reached the highest signal at 24 h. From PET/CT images with subcutaneous and orthotopic colon tumor-bearing mice, clear radioactivity could be seen in tumors, which suggested the successes of TEX accumulation in tumors. TEX@DOX@ALA group with photodynamic therapy and chemotherapy had the best tumor inhibition effect compared with the other groups, with the longest survival time (36 days, 37.5%). No significant damage was found on histological observation and the blood biochemical analysis, which suggested the safety of the multi-drug loaded exosomes. CONCLUSIONS: We successfully engineered an exosome-based nanoprobe integrating PET imaging components and therapeutic drugs. This drug-loaded exosome system may effectively target tumors and enable synergistic chemotherapeutic and photodynamic antitumor effects.