Although expanding spacing is often regarded as the most effective practice schedule, studies comparing equal and expanding spacing have yielded mixed results. The present study set out to examine whether the amount of spacing and the retention interval may influence the effects of expanding and equal spacing on second language (L2) vocabulary learning. One hundred and twenty-eight Japanese college students studied 20 English-Japanese word pairs. The type of spacing (expanding and equal) and the amount of spacing (massed, short, medium, and long) were manipulated. Results demonstrated a limited, yet statistically significant, advantage of expanding spacing. The finding is significant because this is the first L2 study to find the superiority of expanding over equal spacing. The main effect of the amount of spacing was also significant, producing large effect sizes. Taken together, the results suggest that expanding spacing may facilitate vocabulary learning, although introducing spacing may have a larger effect.