Temperature dependence of the third-order magnetic susceptibility χ M ( 3 ) along the a,[110] and c-axis were measured on a single-crystalline sample of an antiferroquadrupolar (AFQ) ordering compound DyB 2 C 2 . The χ M ( 3 ) values are negative below 80K in all directions. For H||c,χ M ( 3 ) has a minimum around 28K and shows divergent behavior at T Q =24.7K with decreasing temperature, while χ M ( 3 ) for H||a and H||[110] decrease monotonically as temperature decreases, but these decreasing rates increase slightly at T Q .