Objective: To investigate malaria infections in asymptomatic legal migrant workers and symptomatic patients in Thamaka, Kanchanaburi Province. Methods: This study was conducted during April 26-29, 2008 using thick and thin blood Giemsa's stained. A total of 671 samples were collected in asymptomatic migrant workers and 38 samples in symptomatic patients in the same period. Results: The results showed the prevalence rate was 1.64% (11 out of 671 samples) in asymptomatic migrant workers and P. vivax infections were found to be dominant (81.8%). Age group of infections showed between 16-42 years as a high risk of infection. Female: Male ratio was 1: 1.3. The infection rate was 35.7% (10 out of 38 samples) in symptomatic patients with the highest infection being P. falciparum (80.0%). Age group of infections between 13-36 years. Male: Female ratio was 1: 1.4. About 43% of malarial infections came from Mohlumyai area, Myanmar. Conclusions: The high rate of malarial infections in Thamaka District still need surveillance, especially as migrant workers may spread malaria to the people living in this area if vector present. © 2012 Asian Pacific Tropical Medicine Press.