© 2014 American Chemical Society. Five novel generations of phosphorus dendrimers based on a cyclotriphosphazene core with stable TEMPO radicals end groups have been synthesized and studied by EPR, SQUID, 1H NMR, 31P NMR, FT-IR, and UV-vis spectroscopy. The nitroxyl radicals exhibit a strong exchange interaction, which depends on the dendrimer generation and the temperature. An |fms| = 2 transition has been observed in each generation in dilution conditions demonstrating the intramolecular origin of the radicals interaction. There exists a direct proportionality between the EPR |Δms| = 2 transition intensity and the number of radicals by generation; consequently, the utility of EPR for the determination of the substitution efficiency on dendrimers by paramagnetic species is quite good. From the UV-vis characterization, we have observed that the molar extinction coefficient value is also proportional to the number of TEMPO groups. The magnetic properties of the zero, first and fourth generation dendrimers studied by SQUID magnetometry show antiferromagnetic interaction between radicals.