Display omitted •To detect carbaryl pesticides, simple colorimetric detection method is developed based on azo-coupling reaction.•Carbaryl pesticide can be detected selectively within 1 min with other carbamates.•Limit-of-detection for carbaryl is lower than permissible exposure level (∼15 ppm).•The carbaryl concentration are estimated in real fruit samples with natural interferences. For rapid detection of carbaryl pesticides, we developed a simple colorimetric detection method based on azo-coupling reaction. Pretreating carbaryl pesticides with an organic base yielded 1-naphthol, which readily reacted with a diazonium salt with a dramatic color change. Since the resulting azo dye can further change color with the organic base used in the pretreatment, phosphoric acid was added to suppress the confounding colorimetric response. We report that this new colorimetric method can selectively detect carbaryl pesticides from other carbamate pesticides within a minute. Moreover, carbaryl can be detected below 10 parts per million (ppm), which is below its permissible exposure limit (∼15 ppm). Finally, we successfully estimated the concentrations of carbaryl pesticides on fruit samples in the presence of natural interferences.