The reactions of octachlorocyclotetraphosphazene, N4P4Cl8, with N-alkyl-N-mono-ferrocenyldiamines, FcCH2NH(CH2)nNHR1 [n = 2, Fc = ferrocene, R1 = Me (1); n = 2, R1 = Et (2) and n = 3, R1 = Me (3)], led to the formation of monoferrocenyl-spirocyclotetraphosphazenes (4–6). When the reactions were carried out with excess pyrrolidine, morpholine and 1,4-dioxa-8-azaspiro[4,5]decane (DASD), the fully substituted products (4a–6c) were obtained in high yields. The structures of all the phosphazene derivatives were characterized by MS, FTIR, 1H, 13C and 31P NMR, HSQC and HMBC techniques. The crystal structures of 4a and 5a were determined by X-ray crystallography. The electrochemically reversible one-electron oxidation of Fc redox centers was observed for cyclotetraphosphazenes. The fully substituted phosphazenes (4a–6c) were evaluated for their antituberculosis activity against reference strain Mycobacterium tuberculosis H37Rv, and compounds 4a–6a and 5c were found to be active. The antibacterial activities of phosphazenes 4a–6c against G(+) and G(−) bacteria and their antifungal activities against yeast strains were carefully scrutinized. The results indicate that compounds 4a–6a, 6b, 4c and 5c are very effective against yeast strains. The anticandidal activities of 6a and 6b make them promising anticandidal agents. The interactions of these compounds with plasmid DNA and their cytotoxic activity against L929 fibroblast and DLD-1 colon cancer cell lines were also investigated.