Introduction: Leptospirosis is a major neglected public health problem and is highly underreported in India. It is a common cause of the acute febrile illness (AFI), but accurate diagnosis is quite challenging and often delayed because of overlapping symptoms with many other infectious diseases, and limited access to laboratory diagnosis. The aim Aim: of the study was to assess the proportion of Leptospira infection among patients suffering from AFI in West Bengal and to analyse socio-demographic characteristics, clinical features, and laboratory parameters of leptospirosis cases. Materials and methods: Serum samples were collected from 350 hospital-admitted patients suffering from AFI (fever >five days ≤ two weeks) but without any identifiable cause and tested for Leptospira IgM using PanBio Leptospira IgM ELISA kit. Clinical features, laboratory parameters and epidemiological data were collected from each patient and analysed. 91(26%) out of 350 fever cases tested positive for Leptospira IgM ELISA. Most of them were Result: male and belonged to the age group of 31–60 years (42.85%) and 16–30 years (30.76%). Common symptoms were fever (100%) myalgia (76.92%), headache (70.32%), icterus (69.23%), vomiting (67.03%) and pain abdomen (65.93%). Conclusion: Leptospirosis is a common cause of acute undifferentiated febrile illness in West Bengal. Our findings demonstrated the importance of active surveillance of leptospirosis among cases of acute febrile illness to facilitate its early detection and prevention of complications.