In this study, the quantitative amount of 5-hydroxyindoleacetic acid (5-HIAA) was determined at poly (p-amino benzene sulfonic acid) (p-ABSA) modified glassy carbon electrode. The redox property of 5-HIAA was investigated by cyclic voltammetry. The cyclic voltammograms showed that the redox reaction of 5-HIAA was irreversible. Scan rate study showed that the redox reaction of 5-HIAA was controlled by both diffusion and adsorption on the poly (p-ABSA) modified sensor. Differential pulse voltammetry technique was used for the quantitative analysis of 5-HIAA in phosphate buffer solution at pH 7.00. The linear working range of the calibration graphs was determined as 1×10^-5–9×10^-5 M (R², 0.9912), and the detection limit was determined as 5.3×10^-7 M. Recovery values ​​in the analysis of urine samples were between 99.4% and 103.0%. The results showed that the modified sensor can be applied to the determination of 5-HIAA in the presence of ascorbic acid. The proposed sensor is promising for routine analysis due to its high selectivity, reproducibility, long-term stability, and high recovery values in biological samples.