BACKGROUND AND AIM: Horses have a strategic and vital role to play in the lives of the people of Sumba Island, East Nusa Tenggara Province. They act as social animals that are involved in death ceremonies, horse races, and during pasola, thereby supporting tourism, and are given away as dowry in wedding ceremonies. This study aimed to investigate the prevalence of trypanosomiasis among horses in four districts of Sumba Island by examining clinical symptoms and detecting parasites, antibodies, and other factors that are related to Trypanosoma evansi infection in horses. MATERIALS AND METHODS: We studied a total of 211 horses that belonged to 88 clinical hobby breeders. Giemsa-colored smears and serum were examined in order to detect antibodies using card-agglutination tests (CATT). The study was conducted during the rainy season that lasted from January to March 2017. Potential risk factors such as the species, sex, origin of the livestock, how the livestock were maintained, and the farmers' knowledge concerning trypanosomiasis were recorded using questionnaires. Data were collected annually for three years from 2010-2012 and repeatedly analyzed by a Chi-square test. RESULTS: Clinical signs of trypanosomiasis were found in 34 horses; blood smears were examined using Giemsa staining and negative preparations were obtained at a frequency of 0.0% (0/211). The CATT results generally showed that 13.3% (28/211) of the samples were seropositive for antibodies to T. evansi; the highest percentage, 16.67% (8/48), of seropositivity was found in the West Sumba District, and the lowest, 12.0% (5/50), was found in Southwest Sumba. The incidence of trypanosomiasis was higher (75% [21/28]) among female hip horses; horses with 1-5 years of experience were more susceptible to a T. evansi infection (46.4% [13/28]). In general, farmers on Sumba Island knew of trypanosomiasis (89.8% [79/88]), and 69.3% (61/88) of the farmers reported that their livestock was sick. This study was the first serological study conducted on trypanosomiasis in horses of Sumba Island after the surra outbreak in 2010-2012. There were 3% of farmers who were willing to provide the government with information on implementing a prevention program and controlling the spread of surra on the island. CONCLUSION: The diagnoses of surra disease were made based on clinical symptoms and parasitological examinations. CATTs could be used to diagnose T. evansi infection in horses.