A possible side-effect of exposure to non-native sounds is a change in the way we perceive native sounds. Previous studies have demonstrated that native speakers' speech production can change as a result of learning a new language, but little work has been carried out to measure the perceptual consequences of exposure. The current study examined how intensive exposure to Spanish intervocalic consonants affected Chinese learners with no prior experience of Spanish. Before, during and after a training period, listeners undertook both an adaptive noise task, which measured the noise level at which listeners could identify native language consonants, and an assimilation task, in which listeners assigned Spanish consonants to Chinese consonant categories. Listeners exhibited a significantly reduced noise tolerance for the Chinese consonants /l/ and /w/ following exposure to Spanish. These two consonants also showed the largest reductions in Spanish to Chinese category assimilations. Taken together, these findings suggest that Chinese listeners modified their native language categories boundaries as a result of exposure to Spanish sounds in order to accommodate them, and that as a consequence their identification performance in noise reduced. Some differences between the two sounds in the time-course of recovery from perceptual adaptation were observed.