Objective To investigate the inhibition performance of 4-Phenylthiosemicarbazide (4-PTC) for Q235 steel in 1 mol/L HCl solution. Methods A new corrosion inhibitor, 4-PTC, was synthesized using phenyl isothiocyanate and hydrazine hydrate as raw materials. The synthesized compound was confirmed by melting point, 1H-NMR and IR methods. The corrosion inhibition efficiency of 4-PTC was measured by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy and scanning electron microscope methods. Results The results of weight loss measurements showed that the inhibition efficiency of 4-PTC could reach up to 85.9% at the concentration of 1.0 mmol/L and the adsorption process obeyed the Langmuir adsorption isotherm, forming monolayer. The value of ΔGads was -35.60 kJ/mol, which indicated that the adsorption mechanism involved both chemisorption and physisorption. The potentiodynamic polarization plots showed that 4-PTC acted as a mixed type inhibitor and showed more pronounced influence in the cathodic polarization plots compared to that in the anodic plots. The inhibition efficiency of 4-PTC could reach up to 83.6% at the concentration of 1.0 mmol/L. Meanwhile, the electrochemical impedance showed that the charge transfer resistance increased with the increase of the 4-PTC concentration, while the value of double layer capacitance decreased. This phenomenon showed that the corrosion rate decreased and the inhibition efficiency increased. The inhibition efficiency of 4-PTC could reach up to 84.7% at the concentration of 1.0 mmol/L. The scanning electron microscope method showed that the 4-PTC had excellent inhibition behavior and could protect the Q235 steel. Conclusion 4-PTC showed good inhibition efficiency for Q235 steel in HCl solution.