A novel process for preparing chromium dioxide of substantially high purity as well as composites of CrO.sub.2/Cr.sub.2O.sub.3 and CrO.sub.2/Cr.sub.2O.sub.5 following a sequence of simple steps. The process does not require pressure as a control parameter during the process of synthesis. No chemical modifier has been used to bring down the working pressure during synthesis. Fairly hard sintered pellets of CrO.sub.2 can be obtained without introducing any detectable impurity phase that usually appears during the process of sintering. Further, CrO.sub.2/Cr.sub.2O.sub.3 and CrO.sub.2/Cr.sub.2O.sub.5 composites have also been prepared where the fraction of insulating Cr.sub.2O.sub.3 or Cr.sub.2O.sub.5 in metallic CrO.sub.2 can be easily controlled. Significant negative magnetoresistance is found in pure CrO.sub.2 (5% MR) as well as CrO.sub.2/Cr.sub.2O.sub.3 (33% MR) composites near room temperature. The MR studies on the CrO.sub.2/Cr.sub.2O.sub.5 composites have been done and significant negative MR (22%) has been found in CrO.sub.2/Cr.sub.2O.sub.5 composites near room temperature.