The persistence and biodegradation of prometryne in the liquid culture of the fungus Phanerochaete chrysosporium were studied. The fungus was grown in liquid culture treated with different concentrations of prometryne (0, 1, 10, and 50 ppm) and incubated at 28°C in a shaking incubator. Samples were taken periodically (0, 1, 2, 4, 8, 10, 15, 30, and 45 days) to study the herbicide's persistence and degradation process. Results revealed that the time intervals for a 50% disappearance rate of prometryne were 3, 8, and 13 days for the treatments of 1, 10, and 50 ppm respectively. Prometryne was degraded by the fungus into six by-products with distinct chromatographic properties, yielding Rf values of 0.12, 0.21, 0.32, 0.42, 0.50, and 0.74 on the TLC plates. These by-products were identified by IR spectroscopy as various N-dealkylated and hydroxylated derivatives.