This study was conducted at South Ari Woreda, South Omo Zone, Southern Nations, Nationalities and Peoples Regional State of Ethiopia. Due to poor adoption of improved (BH-140) maize variety and different constraints, the maize production and productivity is low in the study area. The aim of this study was to identify the determinants of adoption improved (BH-140) maize variety and its management practice in the study area. By using a systematic random sampling technique a total of 142 sample households were selected from 4 kebeles were interviewed by using a structured interview schedule. Qualitative data were collected using group discussion and key informants interview. Secondary data for this study obtained from the book, journals, published and unpublished documents. Data were analyzed using SPSS.version.16, descriptive statistics, Chi-square and t-test and logistic regression (binary logit) model. The descriptive statics result of the study indicated that about 48.59% of the sample respondents were non-adopters of the improved (BH-140) maize variety, while 51.41 % adopters. The status of management practices was found below research recommendation because of inadequate extension service, a high cost of fertilizer, pest, and lack of credit access. Farmers selection criteria for improved (BH-140) maize variety were high yielding, early maturity, disease resistance, price advantage, storability and market demand 42.95%, 39.46%, 8.45%,5.63% ,2.11%,1.4% respectively. Results of the logistic regression analysis indicate that among 14, identified explanatory variables, 8 of them education and, contact with extension agent significance at1%, sex Livestock, Income, demonstration were significant at 5% and credit were significant at 10% and positively affect adoption of improve maize technologies, Whereas, distance from market center significant at 10% but negatively affect the adoption. Based on this finding, the study suggests that the government, agricultural and natural resource and research center should focus on strengthening the existing extension service; provision of quality seed, adapt other new variety, credit service in maize farming. Moreover, attention should be given to those significant variables which have a potential impact in determining farmer's adoption decision in the study area.