Background: Optimal infant feeding is critical for children’s growth and development during their first years of life. Plenty of evidence on ineffective breastfeeding techniques, yet the problem is still deep-rooted and requires further research in Ethiopia. Objective: To determine the proportion of ineffective breastfeeding techniques and associated factors among breastfeeding mothers who gave birth in the last 6 months in Sinan Woreda. Design and methods: A community-based cross-sectional study was conducted from March 10 to April 8, 2021 with a total of 389 samples. A computer-generated simple random sampling was used to select mothers. An observational checklist and interviewer-administered questionnaires were used. EpiData 4.2 for data entry and SPSS 25 for cleaning and analysis were used. Variables with a p-value < 0.05 and 95% confidence interval (CI) corresponding adjusted odds ratio (AOR) were used to identify factors of ineffective breastfeeding techniques. Results: The proportion of ineffective breastfeeding techniques was 66.8%. The mean (SD) age of mothers was 29.4 ± 5.95 years. No formal education [AOR: 5.88 (95% CI: (2.97, 11.65)], primipara [AOR: 4.34 (95% CI: 2.25, 8.36)], home delivery [AOR: 3.02 (95% CI: 1.12, 8.14)], not received breastfeeding counseling during antenatal care [AOR: 4.94 (95% CI: 1.83, 13.36)], breast problem [AOR: 2.62 (95% CI: 1.25, 5.48)], and breastfeeding experience [AOR: 1.82 (95% CI: 1.01, 3.28)] were statistically significant factors. Conclusions: The proportion of ineffective breastfeeding techniques 66.8% was unacceptable. Socio-demographic and maternal health care services were identified factors. Strengthening maternal care, improving health education and promotions, and designing appropriate strategies were required.