An all-organic Bacterial Cellulose-Conducting Polymer (BC)-PEDOT:PSS composite, impregnated by Ionic Liquids (ILs), is investigated as a mass sensor. The sensor works as a vibrating transducer, in cantilever configuration and produced a voltage signal as a consequence of the applied deformation. The influence of the added-mass on the frequency response of the system is exploited for estimating the value of the measurand. Though generating properties of composites based on BC have been already demonstrated, this is the first report showing the possibility of mass sensing by using such composites. The sensing system is based on cheap, flexible, and ecofriendly materials suitable to the realization of next to come smart ubiquitous sensing systems. The performance of the sensing system are shown in the paper.