Covalent organic framework (COF) thin films have been successfully prepared and utilized as a channel material in electrical double-layer (EDL) electrochemical transistors. 4,4′-azodianiline (Azo) and 1,3,5-triformylphloroglucinol(Tp) precursors are introduced to prepare azo (NN) functionalized ß-keto-enamine COF (Tp-Azo) thin films. The EDL transistor exhibits a switching ratio of 103 times, a low threshold voltage of 0.6 V, and a field-effect mobility of 0.53 cm2 V−1 s−1. The dynamic behavior of the transistor under different input signals shows responses, which are very similar to the biological synaptic behavior, indicating that the COF devices can be used as artificial synapses. This report opens a new direction in covalent–organic framework development in iontronic applications.