•Electrospun Mn2O3 nanofiber: Breakthrough in zg/mL detection of atrazine.•Facile, label free and ultrasensitive electrochemical platform for detection of atrazine.•Analyte detection in spiked water samples.•Good stability and high degree of selectivity to atrazine.•Able to clearly detect atrazine in presence of interfering compounds (Interference study). Atrazine, a pesticide of chloro-triazine family and a class 3a carcinogen, is known to severely affect human endocrine system. In light of its detrimental environmental effects, ensuring its easy and ultrasensitive detection is highly essential. In this paper, we demonstrate facile and label free electrochemical detection of atrazine, using electrospun manganese oxide nanofibers (MNF). Here, we report an anti-atrazine-antibody based immunosensor, based on low bandgap Mn2O3 nanofibers, for ultrasensitive and highly selective detection of atrazine. The electrospun nanofibers used in this work were characterized using field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and UV–vis Spectroscopy. The proposed platform was able to detect atrazine in the concentration range of 10−21 g/mL, which in comparison to the previously reported atrazine sensors is a fairly superior performance. The observed lower limit of detection (LOD) was 0.22 × 10−21 g/mL, with a sensitivity of 52.54 (kΩ/μg mL−1)/cm2. We have also demonstrated atrazine detection in spiked water samples, so as to demonstrate that the proposed platform is suitable for real-time applications. Furthermore, the sensing platform is label free, comprising of a simple protocol and hence is facile in nature.