CuFe bimetallic nanoparticles were prepared and used as model catalyst for deactivation study in higher alcohol synthesis. The structural evolution of CuFe bimetallic nanoparticles during reaction was investigated. Phase separation of Cu and Fe components was observed directly by STEM-EDS and HRTEM. It was found that CuFe bimetallic nanoparticles with homogeneous dispersion of Cu and Fe components separated into monometallic Cu nanoparticles, Fe 3 O 4 nanoparticles, Fe 3 O 4 nanorods and χ-Fe 5 C 2 in the form of very small crystallites or amorphous layer on Fe 3 O 4 containing nanoparticles and nanorods. The phase separation weakened the synergism between Cu and Fe and led to decreased selectivity to alcohols with time on stream. The correlation between the change of catalytic performance and the structural evolution was also discussed.