Unmet need for family planning in Oromia region was very high (28.9%) compared to other regions in Ethiopia. To address problems associated with unmet need for family planning locally available evidences are essential, however, there were no clear evidences on unmet need for family planning in Tiro Afeta district. This study aims to assess the magnitude and associated factors of unmet need for family planning among currently married women in Tiro Afeta district, South West Ethiopia, 2017. Community based cross sectional study was conducted in April, 2017. A total of 348 currently married women of reproductive age were enrolled from eight villages selected by simple random sampling and using proportional to size allocation. Data were entered using EpiData 3.1 and analyzed by SPSS version 22. Adjusted odds ratios at 95% confidence interval with p-value of < 0.05 were considered as significant variables. Unmet need for family planning among currently married women in Tiro Afeta was 26.1%. Factors significantly associated with unmet need for family planning were: never use of family planning before survey (AOR: 5.09, 95% CI: 2.73-9.50); multiparity (AOR: 3.02, 95% CI: 1.56-5.85); perceived husband's attitude as disapproval (AOR: 2.75, 95% CI: 1.43-5.26); lack of counseling from health workers (AOR: 2.07, 95% CI: 1.11-3.85); and unavailability of Radio and/or Television in the house (AOR: 2.05, 95% CI: 1.15-3.66). Unmet need for family planning in Tiro Afeta was higher than national average but lower than Oromia region. Never use of family planning, women's parity, husband's attitude towards contraceptives, women counseling and unavailability of Radio and/or Television in the respondent's home were significantly associated factors with unmet need for family planning. Therefore, the service providers and the district health office should strengthen counseling and partner involvement to reduce unmet need for family planning.