Among livestock diseases tsetse-transmitted trypanosomosis, have been incriminated as the predominant elements in the extreme deterioration of animal resources in sub-Saharan region; Ethiopia that holds the greatest potential for expanding livestock production. The part of Amaro special district particularly mid and low land is infested with tsetse fly where animal trypanosomosis is a serious threat to livestock production. Thus the objectives of the present study were: to determine the prevalence and impact of bovine trypanosomosis and seasonal density of tsetse flies; the efficacy of Isometamidium chloride on bovine trypanosomosis. The study was conducted from October 2007 to May 2008 in Amaro special district of SNNPR. The study design involved questionnaire survey, seasonal cross sectional studies of tsetse and trypanosomosis and assessment of Isometamidium chloride therapeutic efficacy. The questionnaire survey indicated that trypanosomosis is an important problem following erratic rain fall affecting the animals and impeding agricultural activity of the area. The entomological survey revealed that Glossina pallidipes species was the only prevalent species along with other biting flies (Tabanids and Stomoxys). The apparent density of flies was significantly higher in the late rainy season 1.62 fly/trap/day,2.37 and 1.6 for G. pallidipes, Tabanids and Stomoxys, respectively than the dry season where the density was 0.66, 1.12 and 1.03, respectively. The tsetse fly account 27 %, of the total fly catch Tabanids 42.6 %, and Stomoxys 29 % during late rainy season and 24.7 %, 35 %, 39.9 % during dry season. In the low lands (