4-Chlorophenol removal combining KrCl excimer UV lamp and H2O2 has been studied, using 4-chlorophenol concentrations of 100 and 250 mg L-1 and molar ratios H2O2:4-chlorophenol 1:1, 10:1, 25:1, and 50:1. A ratio of 25:1 achieves the total removal for both 4-chlorophenol and the photoproducts. Comparing these results with those corresponding to the use of excilamp treatment in the absence of H2O2, there is no difference in 4-chlorophenol degradation. The excilamp alone, however, leads to the incomplete removal of photoproducts. Additionally, significant COD decrease is attained in the samples treated with UV/H2O2 and toxicity bioassays with Pseudomonas putida show important toxicity alleviation.