This study investigated the factors affecting Thai taxi drivers' English competence. Altogether, 342 taxi drivers answered questionnaires and performed tasks that measured their English language competency; aiming to find out what the factors are that affect their English competency. The taxi drivers were all Thais sampled from three zones in the Bangkok metropolis. The instruments included the test and the questionnaires. The data collection was carried out during January to May 2016. The structural equation model, based on relevant theories and research findings, was constructed to explain the factors affecting their English language competence. The exogenous factors were their educational background and previous English language training, attitudes towards non-Thai passengers, motivation, and their independent language learning behavior. The results showed that the model was supported by the empirical evidence. The model was fitted with the Chi-square of 53.821, CFI of 0.996, NFI of 0.972, GFI of 0.977, and RMSEA of 0.022. The majority of Thai taxi drivers' English language competence was at the low level (Mean = 2.50). It was also found that their educational background and English language training significantly affected their English competence directly and indirectly.