Cationic N,O-chelating dendrimers functionalised on the periphery with RAPTA-like (ruthenium(II)-arene-1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane) moieties have been synthesised and characterised using NMR and IR spectroscopy, elemental analysis and MALDI-TOF/HR-ESI mass spectrometry. Metallodendrimers from the first to the fourth-generation containing up to 32 peripheral ruthenium-arene-PTA moieties were obtained. Model mononuclear analogues, [{Ru(η⁶-p-cymene)((C₇H₅NO)-κ²-N,O)(PTA)}((CH₂)₃)][PF₆] and [{Ru(η⁶hexamethylbenzene)((C₇H₅NO)-κ²-N,O)(PTA)}((CH₂)₃)][PF₆], have been prepared and their structures were determined by single crystal X-ray diffraction analysis. The cytotoxicities of the metallodendrimers and their mononuclear analogues were established on A2780 and A2780cisR human ovarian carcinoma cancer cells and model human embryonic kidney (HEK) cells.