A two-step synthesis method was used to synthesize a series of N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-Proxyl conjugates as a contrast agent for magnetic resonance imaging (MRI) of solid tumors. The conjugates were characterized by Proxyl content using UV spectroscopy, electron spin resonance (ESR) spectroscopy and size-exclusion chromatography profile using a Fast Protein Liquid Chromatography instrument. The results show that a series of HPMA copolymer-Proxyl conjugates with incremental increase in Proxyl content were successfully synthesized and characterized, coupled with the macromolecular nature of the conjugates indicate that the copolymers have potential in MRI of solid tumors by enhanced permeability and retention effect.