Research questions: Although much research has examined the L1 influence on non-native speech perception and production, few studies have investigated the effect of L1 dialects on L2 speech perception and production (Escudero et al. 2012). To fill this gap, this study investigates the influence of L1 dialects on the perception and production of English tense/lax vowel contrasts by native speakers of Korean from two different dialectal backgrounds, namely Seoul Korean (SK) and Kyungsang Korean (KK). They were chosen based on dialectal factors which differ in their use of vowel duration which potentially affects their perception and production of non-native contrasts. Method: Twenty Korean speakers (10 SK, 10 KK) completed perception and production experiments. In perception, the listeners were tested on their ability to discriminate English tense/lax vowel contrasts in /pVb/ and /pVp/ contexts (Lengeris 2009), evaluating the effect of the shortening of vowels before voiceless stops on their perception in a categorical discrimination test. Production tests examined Korean speakers’ production accuracy of the English tense/lax vowel contrasts in voiced (/CVd/) and voiceless (/CVt/) contexts. Their production accuracy was assessed by native speaker judgments and acoustic analysis. Results: The perception test revealed that SK and KK groups did not differ as a function of L1 dialects, and both Korean groups showed similar patterns of perceptual sensitivity to the target vowels. The effect of context on the discrimination of the English contrasts showed that both SK and KK listeners were sensitive to durational cues. However, Korean listeners were not simply comparing the duration in discriminating the two vowel contrasts. There existed an easier vowel contrast in one context than the other for Korean listeners although the duration difference between the two vowels was similar across contexts (i.e. /pup/-/pʊp/). This suggests that Korean listeners use both durational and spectral cues to discriminate the contrast, and L2 vowel perception is a complex interplay between spectral and durational cues. The production test also showed that SK and KK speakers did not differ in production accuracy, and both Korean groups have difficulty in producing the English tense/lax vowel contrasts in a native-like way. Both Korean groups over-relied on vowel duration to distinguish the English front vowel contrast /i/-/ɪ/ in both contexts, whereas both groups showed no or minimal duration differences in the back vowel contrast /u/-/ʊ/. Conclusions: Korean speakers’ degree of accuracy in perceiving and producing the English tense/lax vowel contrasts, as well as the extent to which their performance influenced by consonantal contexts, did not vary as a function of dialectal background. This suggests that the availability of durational information in an L1 dialect may not affect the process of making use of spectral and durational information in an L2.