This study was undertaken to measure the aerobic biodegradation of phenol using poultry litter and to compare the toxicity of the parent compound with the end product(s). Phenol was aerobically treated with a water extract of the untreated litter or of irradiated litter in order to differentiate between the effects of the microorganisms and other chemical species present in the litter on the biodegradation of phenol. Two concentrations of phenol (10 ppm and 100 ppm) were each treated with three concentrations of leachate (0.2%, 0.5% and 1%). The litter leachate (1%) degraded 10 ppm and 100 ppm phenol by 88% in 8 h and 24 h, respectively. Lag phases were observed for all treatments except with 1% leachate. The lag phase increased as the concentration of phenol increased and decreased with an increase in the leachate concentration. No degradation was observed using the leachate of the irradiated litter. Experiments usingCeriodaphnia dubia, (LD50) andVibrio fischeri, (EC50) showed that the degradation end product (s) were non‐toxic compared with the parent compound.