Identification of the host blood meal of hematophagous insects can provide significant information regarding host preferences and the possibility of the transmission of disease agents. Currently, this knowledge is limited for black flies in the Oriental region. In this study, we used cytochrome b gene sequences for identification of blood meal sources of two black fly taxa, the Simulium asakoae complex and S. chumpornense Takaoka & Kuvangkadilok in Thailand. A total of 4,260 wild adult females were visually screened revealing 24 blood-engorged females from which cytochrome b was successfully amplified in 19 individuals. Comparisons in GenBank database revealed that all are closest to chicken (Gallus gallus) with sequence similarity of >98%. Therefore, these black fly species are feeding on chickens. We also molecularly investigated the hemosporidian blood protozoa genus Leucocytozoon in black flies and found 13 of 19 blood-engorged females positive for this protozoon. Sequence analysis revealed that this Leucocytozoon DNA could be assigned into two previously recognized groups, one with a Leucocytozoon reported from domestic chickens and black flies in Thailand, and another close to the L. schoutedeni. Our results indicate a high possibility that the S. asakoae complex and S. chumpornense are natural vectors of Leucocytozoon.