This study investigates the perception of Spanish vowels: /a e i o u/ and English vowels: / i ɪ ɛ eɪ æ u ʊ oʊ ɑ ʌ/ by native-speakers (NS) of English learning Spanish and NS of Spanish learning English. It analyzes and compares the perception of NS and non-native speakers (NNS) cross-linguistically. The perception of English vowels has been investigated in depth (Bohn & Flege, 1990; Fox, Flege & Munro, 1995; Mitleb, 1984; Munro, 1993), and it has been cross-linguistically analyzed with French and German among other languages primarily with discrimination and identification tasks. Johnson, Flemming and Wright (1993) analyzed the perception of English vowels by NS using a method of adjustment (MOA) task. No previous study, however, has focused on the investigation of Spanish and English vowels using both natural and synthesized data, and NS and NNS in identification and MOA tasks. English NS learning Spanish (n= 54) and Spanish NS learning English (n= 17) completed four tasks in Spanish and four in English whereby they were exposed to both natural and synthesized data (330 synthesized vowels, as in Johnson et al. 1993) in order to analyze spectral differences in the perception of both sound systems, and how the learners’ system may vary from that of the NS. In the natural speech tasks they had to identify the vowels with which they were provided from list of written words, one of which contained the target vowel. In addition, they were asked to select which synthesized vowel sounds resembled the most the ones whose spelling was presented to them in the MOA task similar to the one developed by Johnson et al. (1993). The results obtained indicate that Spanish NS identify English vowels in a less native-like manner than English NS identify Spanish vowels. The method of adjustment tasks with synthesized data yielded average results which indicate that Spanish NS perceive most English vowels with formant values which are different from the ones selected by NS of English. However, English NS perceive Spanish vowels which more closely resemble the ones selected by NS of Spanish