Carbendazim is a systemic, broad-spectrum benzimidazole-type fungicide effective against fungi that compromise the safety/quality of food products (fruits, vegetables, field crops, etc.). Though carbendazim constitutes a major environmental pollutant, hazardous for humans and animals and has been banned in most of European Union and USA, many countries still permit its production and use. Reliable determination of carbendazim levels in water, soil and food samples is therefore necessary to assure compliance with national/European regulations concerning MRLs and consequently minimize health risks for living organisms. In this work, an optical label-free white light reflectance spectroscopy (WLRS) biosensor for fast and sensitive determination of carbendazim is presented. The sensor employs an anti-carbendazim polyclonal antibody developed in-house against a cocktail of commercially available benzimidazole derivatives. The transducer employed is a Si chip with a 1-μm thick thermal SiO₂ on top, and is transformed to biosensing element through immobilization of a suitable benzimidazole-conjugate on the SiO₂ surface, while the determination is based on the competitive immunoassay format. For the assay, a mixture of the antibody with the calibrators or the samples is pumped over the chip surface followed by reaction with secondary biotinylated antibody and streptavidin. The WLRS biosensing platform allows for the label-free, real-time monitoring of biomolecular interactions carried out onto the SiO₂/Si chip by transforming the shift in the reflected interference spectrum caused by the immunoreaction to effective biomolecular adlayer thickness. After optimizing the assay parameters, the sensor was capable of real-time sensitive detection of carbendazim in buffer with LoD: 20 ng/mL, within 28 min total analysis time. The intra- and inter-assay CVs were ≤6.9% and ≤9.4%, respectively. The excellent analytical characteristics and short analysis time combined with its small size render the proposed WLRS biosensor ideal for future point-of-need determination of carbendazim in food and environmental samples.