The prevalence of Plasmodium spp. infection among foreign migrant workers was higher than the annual parasite incidence (API) in Thailand (0.41 per 1000 inhabitants, 0.041%) [14,15]. The reasons for the higher prevalence in Myanmar migrant workers than Thai population may relate to inadequate laboratory services and treatment facilities in Myanmar and the intensive malaria control programme in Thailand during the past five decades. Our data also agree with several studies which reported that malaria infections are common among migrantsin many countries (8.2%-60%) . Regardless the clinical follow-up, in this study these positive cases without any symptoms were defined as the asymptomatic Plasmodium spp. infections based on physical examination including clinical interviews. The presence of these asymptomatic infections in Myanmar workers from Bangkok and Samut Sakorn province may lead to epidemic situation and these two provinces appear to represent the added risk of spreading malaria infections to Thai people. Therefore, laboratory diagnosis, treatment, and controlled population movement need to be promoted further.