Considering the importance of organic functionalization of MOFs, we here report a simple, tunable and efficient one-step post-modification procedure for introducing amino and carboxylic groups into the mesoporous metal-organic framework Al- and Cr-MIL-101-NH2 based on its reaction with alkyl bromides. This procedure allows also access to polyfunctionnalized MIL-101 decorated with both carboxylic and primary amino groups. Other chemical functions, such as alcohols and alkynes, were also successfully introduced by this method.