The pesticide-contg. wastewaters from rye-potato, wheatbeet, and fruit farms were treated with Fenton reagent optionally under Hg lamp light illumination to oxidize the organic matter contd. The changes in chem. 0 demand (COD, dissolved organic C (DOC), biodegrability, acute toxicity biodegradability, acute toxicity towards Vibrio fischeri bacteria and the effect on soil respiration were detd. The addition of the raw wastewater to soil resulted in an increase in 0 consumption for the soil respiration but only in the first period (5 days) of the experiment. Both COD and DOC values were considerably reduced and the biodegradability was increased when the wastewaters were treated with the Fenton reagent especially under light The treatment resulted also in decreasing pH (acid formation) and acute toxicity of the wastewater.