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Dissolved oxygen (DO) in the electrolyte of aqueous zinc ion batteries (AZIBs) can cause irreversible side reactions in zinc metal anode. Therefore, the accurate detection of the DO concentration in the aqueous electrolyte is crucial for the performance promotion and mechanistic studies of AZIBs. Herein, organic electrochemical transistor (OECT) based DO sensors are developed by utilizing a carbon fiber (CF) derived CF/platinum/Nafion/polydimethylsiloxane composite as the gate electrode and amine-doped poly(3,4-ethylenedioxythiophene): polystyrene sulfonate as the channel semiconductor. Operating at a gate-source voltage of −0.1 V and a drain-source voltage of −0.025 V, the OECT-DO sensor demonstrates a high sensitivity (141 mV decade−1), a low detection limit (0.0011 mg L−1), a wide linear range (0.027–8.7 mg L−1), and good stability, which are attributed to the transconductance capability of OECT. The exceptional performance of the OECT-DO sensor enables the accurate monitoring of DO content in aqueous zinc sulfate electrolyte, which provides an opportunity to gain an insight of the impact of DO concentration on the zinc metal electrode. This study not only provides a cost-effective and efficient solution for detecting DO concentration in aqueous electrolytes, but also explores the potential applications of OECT sensors in the energy storage devices. • OECT sensor for detecting dissolved oxygen (DO) in aqueous electrolyte was fabricated for the first time. • The transconductance capability of OECT-DO effectively improved its DO sensing performances. • OECT-DO showed high sensitivity, low detection limit, wide linear range, and good stability. • The influence of DO in aqueous electrolyte on zinc-ion battery was studied with OECT-DO. [ABSTRACT FROM AUTHOR]