The objective of this work was to determine the retention of pesticides in membrane filters used for the separation of suspended solids from solutions. Five types of filter materials were tested: cellulose acetate, nylon, polyethersulfone, polyvinylidene fluoride (PVDF), and polytetra‐fluorethylene (PTFE). Five aqueous solutions of pesticides with initial concentrations of 9.5 μg/L were studied: atrazine (6‐chloro‐N2‐ethyl‐N4‐isopropyl‐1,3,5‐triazine‐2,4‐diamine), isoproturon (3‐(4‐isopropylphenyl)‐1,1‐dimethylurea), mecoprop ((RS)‐2‐(4‐chloro‐o‐tolyloxy)‐propionic acid), 2,4‐D ((2,4‐dichlorophenoxy)acetic acid), and bentazone (3‐isopropyl‐1H‐2,1,3‐benzothiadiazin‐4‐(3H)‐one 2,2‐dioxide). Detectable losses of pesticides were measured on all the tested filter materials. Cellulose acetate filter, nylon filter, and polyethersulfone filter retained between 3 and 90% of all five tested pesticides. On PVDF filter and PTFE filter the retention was limited, as only two (isoproturon and mecoprop) out of five pesticides was retained with a maximum retention of 4.2% for isoproturon on the PVDF filter. In the present study no correlation between retention by filters and pesticide solubility in water was observed. The results also demonstrate that pesticides with relatively high solubility and low octanol‐water partition coefficient (Kow values) can be strongly retained by synthetic filter materials.