The work being reported is the first electrochemical sensor for tetrodotoxin (TTX). It was developed on a glassy carbon electrodes (C) that was modified with poly(4-styrenesolfonic acid)-doped polyaniline film (PANI/PSSA). An amine-end functionalized TTX-binding aptamer, 5′-NH₂-AAAAATTTCACACGGGTGCCTCGGCTGTCC-3′ (NH₂-Apt), was grafted via covalent glutaraldehyde (glu) cross-linking. The resulting aptasensor (C//PANI⁺/PSSA-glu-NH_2-Apt) was interrogated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in sodium acetate buffer (NaOAc, pH 4.8) before and after 30 min incubation in standard TTX solutions. Both CV and EIS results confirmed that the binding of the analyte to the immobilized aptamer modulated the electrochemical properties of the sensor: particularly the charge transfer resistance (R_ct) of the PANI⁺/PSSA film, which served as a signal reporter. Based on the R_ct calibration curve of the TTX aptasensor, the values of the dynamic linear range (DLR), sensitivity and limit of detection (LOD) of the sensor were determined to be 0.23–1.07 ng·mL⁻¹ TTX, 134.88 ± 11.42 Ω·ng·mL⁻¹ and 0.199 ng·mL⁻¹, respectively. Further studies are being planned to improve the DLR as well as to evaluate selectivity and matrix effects in real samples.