This paper presents a detailed study of large grains carried out by transmission electron microscopy in two WC-Co alloys, one W rich and the other C rich. In the W rich alloy, some large grains are found in contact with the η phase while no connection of the large grains with graphite particles can be pointed out in the C rich alloy. The C content greatly influences the morphology of large grains: they are flatter in the C rich alloy with smoother interfaces. Whatever the C content, they contain few dislocations compared to matrix grains except in a small area where a dense network is often present. One or even several small WC grains with a small angle misorientation or with a Σ=2 coincidence relationship are often found inside the large grains. They have likely been engulfed during the growth of the large grains owing to the low boundary energy.