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<p>The photochemical and sonochemical degradation of aqueous solutions of pyridine, a common refractory pollutant in wastewater effluents, have been investigated by means of ultraviolet (UV), ultrasound (US), UV/H₂O₂,and US/H₂O₂ irradiation processes. The pure photochemical process were demonstrated to be efficient for degradation of low initial concentrations of pyridine (10 ppm). Sonochemical degradation proceeded very slowly, leading to less than 53% of pyridine removal after 200 min. The degradation efficiency was increased with increasing H₂O₂ concentration; however, the marginal benefit became decreasing with further increasing of H₂O₂ due to the scavenging effect of excess H₂O₂. The kinetics of photochemical and sonochemical degradation of pyridine were found to follow a first-order rate law. A possible degradation pathway for pyridine was also proposed.</p>