Due to the severe lethal effect of organophosphate (OP) compounds such as nerve agents, which irreversibly inhibit the activity of acetylcholinesterase (AChE), rapid on-site detection is essential. In this thesis, we developed a foldable paper-based analytical device (PAD) that was able to detect an AChE inhibitor in a semi-quantitative manner with simple procedures in the field. An angle-based readout of the yellow area in the paper channel was used for the semi-quantitative analysis with the naked eye. The yellow area on the paper channel was produced by the reaction of H2O2 from the enzymatic reaction and cerium oxide nanoparticles (nanoceria) immobilized on the ring-type paper channel. All reagents were pre-coated on the pop-up card shaped PAD to minimize the manual steps for dealing with multiple reagents such as sample mixing and sequential enzyme reactions. After confirming the optimal conditions, we could semi-quantitatively analyze a nerve agent simulant named dimethyl-methylphosphonate (DMMP) as an AChE inhibitor, by simply reading the angle of the yellow area in the paper channel. The foldable paper-based device proposed here would serve as a valuable tool that allows unskilled people to semi-quantitatively analyze AChE inhibitors, including nerve agents and OP pesticides.