Background: In sub-Saharan Africa (SSA), pregnancy and childbirth continue to be viewed as solely a woman’s issues. Increasing partner participation and encouraging joint decision making in maternal health care may provide an important strategy in reducing maternal mortality and morbidity.Objective: To assess the level of male partner involvement in Birth Preparedness and Complication Readiness (BPCR) and its association with women’s use of institutional delivery among mothers who had a child less than 12 months in West Arsi Zone, South Ethiopia Methods: Institutional based cross-sectional study was conducted in West Arsi Zone South Ethiopia in 2019. Systematic random sampling technique was used to select the study subjects. Data was collected using interviewer administered structured questionnaire. Binary and multivariable logistic regression was applied for the analysis of each of the independent variables against the dependent variable. The association between male involvement in BPCR and women’s use of institutional delivery was done. The results were reported using crude and adjusted odds ratio (OR) with their 95% confidence interval. Results: More than half of male partners, 407 (54.3%) accompanied their wife during ANC follow up at least ones for the last pregnancy. Slightly more than three fourth, 571 (76.1%) of male partners involved in BPCR for the last pregnancy. Fife hundred fifty-four (73.9%) of the mothers gave birth in the health institution for the most recent child. Male involvement in BPCR (aOR = 18.7, 95% CI (11.1 – 31.6), joint decision making about place of delivery (aOR = 3.2, 95% CI: 1.76 – 5.7), urban residence (aOR = 2.2, 95% CI: 1.32 – 3.7) and having two or less under-five children (aOR, 95% CI: 2.7 (1.4 – 5.3) were associated with women’s use of institutional delivery. Conclusion: More than three fourth of male partners involved BPCR. Male involvement in BPCR, joint decision making about place of delivery, urban residence and having ≤ 2 under-five children were associated with women’s use of institutional delivery. Designing and implementing health education on the role of male partner in maternal health care is mandatory. Empowering rural mothers to use health institutions for delivery and birth spacing may improve the magnitude of institutional delivery.