The behavior of herbicides CNP (chloronitrophen), molinate and simetryne in soil and in surface water was investigated by using a model paddy field (an ordinary culture and a bare ground) under the conditions of draining water at a controlled rate. Estimated half-life of herbicides CNP, molinate and simetryne in soil was 7-15 days, 5-20 days and 5-20 days, respectively. These herbicides detected in effluent water were 5-7ppb, 1300-1500ppb and 300-360ppb at the maximum concentration, respectively. It was estimated that the total amount which flowed out from the paddy field with surface water was 1.3-1.6% in CNP, 23-27% in molinate and 22-26% in simetryne of the applied one. The similar residue pattern of each herbicide in water was observed between an ordinary culture and a bare ground. Throughout this investigation, the highest concentration of CNP amino derivative observed in soil corresponded to 16% of the CNP applied first (a major portion of it was in the fraction of soil bound residue), and that in water below a detectable level.