Dissertation (MSc Midwifery)Background: Gestational diabetes mellitus (GDM) is rapidly increasing worldwide. Globally, 17.8 million pregnancies are complicated by GDM. Recently, Tanzania has experienced a dramatic increase in the prevalence of GDM ranging from 0% in 1993 to 19.5% in 2017 in different parts. GDM screening is not part of the routine antenatal services in Tanzania. This contributes to scarcity of data addressing the magnitude and predictors of GDM in Tanzania. Objectives: To determine the prevalence and predictors of GDM among pregnant women attending antenatal clinics in Dodoma Region, Tanzania. Methodology: A cross-sectional study was conducted in Dodoma region, Tanzania from April to May 2018 among pregnant women visiting Bahi, Chamwino, Makole health centers and Chamwino dispensary. Convenient sampling was used to select the region, district and health facilities that provide ANC in Dodoma region. Simple random sampling was used to select study participants. Screening and diagnosing of GDM were performed using the 2013 WHO criteria. Analysis was done using SPSS version 22 to determine the prevalence and predictors of GDM. Results: Among 600 expected sample size, 596 participated in the study, and 582 of them were analyzed successfully. The response rate was 99.3%. The prevalence of GDM was 29.2% (n = 170), higher prevalence was found in urban 33.8% (n = 124) than in rural area 21.4% (n = 46). Predictors of GDM were maternal age ≥ 35 years (AOR= 2.775), low physical activity level (AOR= 4.684), alcohol use (AOR=4.437), non-healthy diet (AOR=2.262), lack of awareness on GDM (AOR= 3.406) and family history of diabetes (AOR=2.455). Conclusion: Prevalence of GDM is relatively high in Dodoma region, contributed by advanced maternal age, family history of diabetes, inactive life style, unhealthy diet and lack of awareness regarding GDM. These findings indicate the need for raising awareness, screening and intervening for GDM in the community.