The age at which people acquire a word influences word recognition, known as the age of acquisition (AoA) effect. In the first language (L1), AoA effects are widely found in various languages and experimental tasks. Arbitrary Mapping Hypothesis proposes that AoA effects reflect the loss of network plasticity during the learning of mappings between input and output representations. It predicts that the AoA effect appears (or is larger) when the input-output mapping is arbitrary/inconsistent, relative to consistent input-output mapping. The present study examined how these predictions generalised to the second language (L2). We explored whether the L2 AoA effect was modulated by spelling-sound consistency in Chinese-English bilinguals, adopting a delayed word naming task. The results showed that the mapping consistency modulated the L2 AoA effect on the N170, P200 and N400 components. L2 AoA effect was insignificant in the consistent condition but was significant in the inconsistent condition: late-acquired words elicited larger N170, smaller P200, and larger N400 compared to early-acquired words. These findings suggest that L2 AoA effects occur in the spelling-sound connections, providing direct evidence for the Arbitrary Mapping Hypothesis.