Quinazoline and its derivatives have drawn much attention in the development of potential antitumor agents. Here, we synthesized a series of 1,2,3-triazole derivatives of quinazoline at the C6 position and evaluated for their cytotoxic activity in various human cancer cell lines. We found that compound <b>5a</b> was the most cytotoxic to HCT-116 cells (IC<sub>50</sub>, 0.36 μM). Target profiling found that <b>5a</b> directly binds to both the autophagy-associated protein SQSTM1/P62 and the E3 ligase RNF168, promoting their interaction. Consistently, <b>5a</b> treatment induces a decrease in RNF168-mediated H2A ubiquitination and compromises homologous recombination-mediated DNA repair, thus increasing the sensitivity of HCT-116 to X-ray radiation. Moreover, <b>5a</b> suppressed xenografted tumor growth in mice in a dose-dependent manner. Taken together, the 1,2,3-triazole derivative of quinazoline <b>5a</b> may serve as a novel compound for tumor therapy based on its role in promoting a P62/RNF168 interaction.