In Brazil, polysaccharide–protein conjugate vaccine against Neisseria meningitidis group C (MenCPS-TT) using hydrazine-activated-tetanus toxoid (TT) as a carrier protein has been developed. Because of the toxicity of hydrazine in humans, it is necessary to monitor this substance's process control step during the vaccine production. The electroanalytical methodology was developed and validated for the determination of hydrazine during the process control of MenCPS-TT vaccine production by differential pulse polarography. The reduction potential was −0.95 V in acetone and sulphuric acid solution. The method presented linear range between 30 and 150 μg L−1and recovery of 93.5 ± 0.8%.