In this study, a novel electrochemical ultrasensitive immunosensor based on disposable benzaldehyde substituted phosphazene polymer (BSPP) modified ITO electrode was developed for interleukin 1β (IL 1β) detection. Aldehyde side groups containing phosphazene polymer (BSPP) synthesized via ring opening polymerization method. These aldehyde groups provided anchoring points for anti-IL 1β antibodies. The production process of the proposed immunosensor was monitored by electrochemical techniques like Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV). In addition, these fabrication steps were characterized by utilizing Scanning Electron Microscopy (FE-SEM) and Atomic Force Microscopy (AFM). Moreover, BSPP polymer layer on the polymer coated electrode surface was investigated by using Energy Dispersive X-ray (EDX). The fabricated immunosensor had a low detection limit (9.3 fg/mL) and a wide linear detection range (0.03-7.5 pg/mL). Moreover, it had good reproducibility (1.82%), excellent repeatability (1.56%), good selectivity and high stability. The results of experiments showed that the BSPP polymer was desirable platform for IL 1β antigen detection in clinical diagnosis and practical applications. The applicability of the suggested biosensor was tested by measuring IL 1β level in human serum and the suggested immunosensor had acceptable results for quantitative analysis.