Increasing oil spill accidents and oil industrial wastewater have led to the frequent occurrence of oily contaminants. To remedy these environmental risks, separating oil/water mixtures by absorbent materials has shown great potential. However, viscous oils are difficult to clean up with conventional materials because of their high viscosity with respect to practical applications. A photothermal (PMSQ)-vinyltrimethoxysilane (VTMS)-polypyrrole (PPy) xerogel was fabricated to heat the viscous oil by utilizing the photothermal property of PPy. The chemical structure and micronano morphology of the obtained composite xerogel were confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, and contact angle goniometry. Experiments of oil adsorption show that the PMSQ-VTMS-PPy xerogel could be applied for viscous oil/water mixture separation, exhibiting excellent properties such as water-repellency, high oil/water separation capacity, adequate buoyancy, good reusability, and easy fabrication. Such a remarkable performance of the PMSQ-VTMS-PPy photothermal xerogel is caused by the fact that crude oil could be heated by harvesting sunlight to reduce the viscosity of oil and achieve the goal of rapidly separating the oil/water mixture. Because of the facile and scalable merits, the one-pot sol–gel method presented is very suitable for industrial uses.