In this study, fourteen new herbicidal ionic liquids (HILs) based on MCPB with 1-alkyl-1-methylpiperidinium cation were synthesized and characterized. The influence of alkyl chain length on physicochemical properties of HILs was described. Additionally, thermal analysis, solubility in ten representative solvents, and surface as well as herbicidal activity were determined. The herbicidal efficacy was tested in greenhouse experiments using common lambsquarters (Chenopodium album L.) and oilseed rape (Brassica napus L.) as test plants. The obtained ionic liquids proved to be more effective than the commercial herbicide. Moreover, the relationship between HILs surface activity and herbicidal efficiency was found.