The objective of the study described in the present paper was to investigate transport and separation properties of ultrafiltration membranes for atrazine solutions in the presence of natural complexing agents (humic and tannic acids). Two ultrafiltration membranes made of various polymer materials were used in the tests. Atrazine concentrations in tested solutions amounted to 1000 mg/m(3). The influence of pH of atrazine solutions as well as the dose of humic and tannic acids on the process efficiency was investigated. The highest efficiency of separation (80%) was achieved for DS-GE membrane at the concentration of humic substances equal to 20 g/m(3).