Polymer nanocomposites based on wide band gap metal oxide nanoparticles are promised functional nanomaterials in many potential applications due to their facile processability. One of their most potential applications is its capability of utilization in the field of photocatalytic oxidation technology. In this respect, fabrication of polyaniline (PANI) nanocomposites based on Co-doped ZnO nanorods is introduced. The Co-doped ZnO nanorods were synthesized using hydrothermal route with molar ratio between cobalt and zinc precursor salts reach to 0.07. XRD and UV–visible absorption measurements confirmed the formation of wurtzite ZnO nanostructured with substitution of Zn sites by Co ions in ZnO host structure. The morphological investigation of PANI/Co-doped ZnO nanocomposites using HR-TEM confirmed the interaction between the synthesized nanorods and PANI matrix. In the present study, the oxidation of synthetic textile dying effluent containing methylene blue has been carried out via PANI/Co-doped ZnO nanocomposites. The attained nanocomposite samples in various Co concentrations labelled as P-CZ0, P-CZ1, P-CZ3, P-CZ5 and P-CZ7 were checked for their catalytic activity for wastewater treatment under the UV-illumination. The influence of various operating parameters was investigated, and the optimal operating conditions were recorded. The experimental results revealed that increasing the dye load reducing the catalytic activity of the dye mineralization. Also, the circulation flow rate is optimized at 147 mL/min at pH 6.0 for the all systems. The experimental data confirms the PANI/ Co-doped ZnO possess the highest catalytic activity which could oxidize 84% of wastewater with a minimum catalyst use of 20 mg/L.