Background. Low back pain (LBP) is the most prevalent musculoskeletal disorder among teachers. The pain, which is widely considered to be caused by occupational activities, has a significant impact on teachers’ quality of life because it results in frequent sick leaves, functional impairment, and early retirement. It is also demanding in terms of treatment costs, individual suffering, and discontinuation of jobs. Therefore, this study assessed the magnitude of low back pain and associated factors among primary school teachers in Mekele City, north Ethiopia. Methods. An institution-based cross-sectional study which included 611 public primary school teachers of Mekele City was conducted from March to April 2015. A multivariable logistic regression analysis was used to identify factors associated with low back pain. The adjusted odds ratio (AOR) with a 95% confidence interval (CI) was used to show the strength of the associations, and variables with a p value of less than 0.05 were considered statistically significant. Results. In this study, the prevalence of low back pain was 74.8% (95% CI: 71.4-78.2). According to the multivariate analysis, the pain was associated with teachers’ sleeping disturbance (AOR = 6.99; 95% CI: 2.20, 13.63), prolonged standing (AOR = 4.78; 95% CI: 3.75, 9.32), and irregular physical exercise (AOR = 1.46; 95% CI: 1.29, 5.10). Conclusion. The study showed that the prevalence of low back pain was high. Sleeping disturbance, prolonged standing during sessions, and irregular physical activity were significantly associated with the problem. Therefore, addressing work-related and individual factors is essential for decreasing the burden.