Low-temperature magnetization (M) measurements down to 0.1 K have been performed in magnetic fields up to 14.5 T for a single piece of a tiny single-crystalline sample (∼0.2 mg weight) of the spin-gap system YbAl3C3. At the base temperature of 0.1 K, several metamagnetic transitions were clearly observed for H ‖ c in the range 6 T < µ 0 H < 9 T whereas only two transitions were observed, one at 4.8 T and the other at 6.6 T, for H ‖ a. At fields above 9 T, the magnetization becomes almost saturated for both H ‖ a and H ‖ c. The present results indicate that a singlet-triplet crossover occurs in a relatively narrow field range, suggesting a rather weak interdimer interaction in spite of the nearly triangular lattice of Yb ions.