A new family of polyanionic poly(alkyl aryl-ether) metallodendrimers decorated with four and eight cobaltabisdicarbollide units have been obtained in high yield by the ring-opening reaction of cyclic oxonium [3,3'-Co(8-(C2H4O)(2)-1,2-C2B9H10)-(1',2'-C2B9H11 )] with alkoxides formed by deprotonation of terminal alcohols in the alpha,alpha'-bis[3,5-bis(hydroxymehyl)phenoxy]-p-xylene, alpha,alpha'-bis[3,5-bis(hydroxymehyl)phenoxy]-m-xylene, alpha,alpha'-bis[3,5-bis-[3,5-bis(hydroxymethyl)phenoxy]methylen]phenoxy ]-m-xylene and alpha,alpha'-bis[3,5-bis-[3,5-bis(hydroxymethyl)phenoxy]methylen]-phenox y]-m-xylene dendrimers. The crystal structure of the precursor alpha,alpha'-bis[3,5-bis(chloromethyl)phenoxy]-p-xylene is also described. Final products are fully characterized by FTIR, NMR, UV vis spectroscopies and elemental analysis. For metallodendrimers, the UV vis absorptions have been a good tool for estimating the experimental number of cobaltabisdicarbollide units peripherally attached to the dendrimeric structure and consequently to corroborate the complete functionalization of the dendrimers.