Display omitted •Bamboo based biochar/montmorillonite composite preparation.•Porous biochar acted as support to host particles of montmorillonite.•The composite exhibited much better compared to raw biochar via nitrates removal. Biochar is a promising immobilization tool for various contaminants in liquid wastes, aqueous solutions and soils. To further improve the sorption characteristics, a biochar/montmorillonite composite was produced and synthesized in an experimental pyrolysis reactor, using bamboo as biomass feedstock. The composite was characterized by physico-chemical and structural methods (FTIR, SEM, SEM/EDX, SSA, Low temperature nitrogen adsorption method). Based on these methods, the successful preparation of a bamboo based biochar/montmorillonite composite preparation has been demonstrated. The particles of montmorillonite were distributed across the biochar surface. The adsorption studies for removal nitrates from aqueous solutions were investigated by a batch method at laboratory temperatures. The experimental data were fitted by three adsorption models (Langmuir, Freundlich and DR; R2 > 0.93). The maximum adsorption capacity achieved by biochar at pH 4, was about 5 mg g−1 and by biochar/montmorillonite composite 9 mg g−1. The results suggest that the bamboo-based biochar/montmorillonite composite can be used effectively in the treatment of industrial effluents or waste water containing anionic pollutants such as nitrates.