This paper describes a measurement method to detect a ppb level of agricultural chemicals within five minutes using a lipid/polymer membrane sensor. Noncharged organic substances have large influences on the adsorption of positively charged lipids to negatively charged membranes. In this study, noncharged agricultural chemicals in the washed vegetables (spinach, broccoli and Japanese basil) solution can be detected. These substances can be detected above 2000 ppb in these solutions. In the case of spinach and broccoli, it can be considered that agricultural chemicals inhibit the adsorption of the adsorbent in solution to the positively charged lipid membrane, because the change rate is below zero. In the case of Japanese basil the agricultural chemicals have a synergetic effect on the adsorption of the adsorbent to the lipid membrane. These results show that noncharged agricultural chemicals can be detected indirectly. We obtained a possibility that agricultural chemicals can be classified before an accurate chemical analysis. It is useful for the evaluating safety of vegetables and fruits.