Aims To evaluate the antibiofilm potential of water‐soluble Moringa oleifera seed lectin (WSMoL) on Serratia marcescens and Bacillus sp. Methods and Results WSMoL inhibited biofilm formation by S. marcescens at concentrations lower than 2·6 μg ml−1 and impaired bacterial growth at higher concentrations, avoiding biofilm formation. For Bacillus sp., the lectin inhibited bacterial growth at all concentrations. The antibiofilm action of WSMoL is associated with damage to bacterial cells. WSMoL did not disrupt preformed S. marcescens biofilms but was able to damage cells inside them. On the other hand, the lectin reduced the number of cells in Bacillus sp. biofilm treated with it. WSMoL was able to control biofilm formation when immobilized on glass surface (116 μg cm−2), damaging S. marcescens cells and avoiding adherence of Bacillus sp. cells on glass. The Bacillus sp. isolate is member of Bacillus subtilis species complex and closely related to species of the conspecific ‘amyloliquefaciens’ group. Conclusion WSMoL prevented biofilm development by S. marcescens and Bacillus sp. and the antibiofilm effect is also observed when the lectin is immobilized on glass. Significance and Impact of the StudyTaking together, our results provide support to the potential use of WSMoL for controlling biofilm formation by bacteria.