The present work reports a simple and single-step hydrothermal synthesis of MoSe2−MoO3 composite for highly sensitive and selective electrochemical oxidation of nitrite. FESEM of the MoSe2−MoO3 hybrid revealed the formation of composite as laminated structure of different sizes piled up together as finger-like MoSe2 bars whilst other physico-chemical characterizations (XRD, FTIR, UV-Vis, XPS) confirmed that co-existence of MoO3 as a major by-product of hydrothermal synthesis. The as-fabricated MoSe2−MoO3 composite based nitrite sensor showed remarkable selectivity and reproducibility with <3s of response time, excellent sensitivity and detection limit of 10.84 A M−1 cm−2 (R2=0.996) and 0.1 μM, respectively, in the range of 2.5–80 μM. The obtained sensitivity can be credited to the high surface area obtained from 1T phase MoSe2 and α phase MoO3 as the sensing material. The developed sensor was effectively evaluated for electrochemical recognition of nitrite in the water samples (potable and tap water) gathered from an industrial area. This new and efficient MoSe2−MoO3 based electrode material offers a new frontier for the progress of a novel composites by simple and single-step approach which can be used for progress of non-enzymatic and inexpensive electrochemical sensors for a wide range of analytical applications. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim