The present experimental research studies whether Thai-English bilinguals’ language experience in their non-native language influences the pattern of language processing of the bilingual lexicon. Two groups of 100 native Thai bilingual speakers with high or low English language experience were asked to perform Stroop Interference Tasks, with the processing of word forms being either Thai or English and the processing in colour naming also being either Thai or English. The results showed that when the processing of word forms was in Thai, there was more intra- than interlingual interference, and that the degree of interference was equivalent between the two English experience groups. When the processing of word forms was in English, the high and the low groups showed more intra- than interbilingual interference; however, the high group showed more interference than the low group did. The results provide evidence that the maximal interference occurs in the processing of the first language and the interference in the processing of the second language is proportional to L2 language experience and language processing of the bilingual lexicon.