We report the giant magnetoresistance (GMR) effect in the first non-pe
rovskite compound Tl2Mn2O7 forming in the pyrochlore structure. Our re
sults, furthermore, show that the GMR is greatly enhanced in the misci
bility gap region of the quasi-binary phase of Tl2Mn2O7 - In2Mn2O7. Ou
r findings should invigorate the exploration of new GMR materials as w
ell as possible utilization of phase mixing to enhance the GMR effect.