A forced choice identification perception experiment using 150 monosyllabic rhyming-word stimulus pairs (with identical consonants and tone) in 4 conditions of white Gaussian noise was conducted to explore vowel confusions in Thai, a language with 9 monophthongs and length (short-long) contrast for all vowels (e.g., /i/-/ii/). Each stimulus containing speech and noise portions is equal in length. Perceptual results of 18 vowels from 36 Thai listeners at a noise level (SNR) of-24dB, where the percent intelligibility is the most interpretable, showed that stimuli with short vowels are more accurately perceived than those with long vowels (93.46 vs. 85.64%) with /oo/ and /ee/ as the most confusable. Interestingly, asymmetrical confusions are observed with few short vowels being misperceived as long vowels, but a number of long vowels misperceived as short. Consistent with previous studies on recognition of English vowels in noise, the findings suggest that perceptual robustness of vowel height (correlating with F1) is higher than vowel front/backness (correlating with F2). The presence of masking noise seems to affect vowel roundness contrast (correlating with lowering of all formants and specially that of F2). Lastly, an analysis for listeners' misidentified responses shows that the listeners generally favor short over long vowels. © 2013 Acoustical Society of America.