Background: Sufficient maternal nutrition is paramount to ensure maternal and fetal wellbeing. It further determines the health of the offspring throughout the lifecycle and prevents adverse health outcomes of the upcoming generation. Therefore, dietary practice and nutritional status of pregnant women and contributing factors among pregnant women visiting antenatal care services at Mettu Karl Hospital, Southwest Ethiopia, were assessed. Methods: Facility-based cross-sectional study was conducted from March to April 2018. A systematic random sampling technique was employed to select 378 study participants. Data were collected via face to face interviews using semi-structured questionnaires. Women Dietary Diversity Score (WDDS) was measured using a qualitative 24- hr dietary recall and nutritional status was assessed by Mid-upper arm circumference measurements. Analyses were done using the statistical package of social science (SPSS version 20). Results: The prevalence of sub-optimal dietary practices was 22% and under-nutrition was 17.5%. Family size >5 [AOR=8.2, 95%CI: 12.383, 46.217] and severe food insecurity [AOR=3.661, 95%CI, 1.289, 10.394] were significantly associated with sub-optimal dietary practices. Being non married woman[AOR= 3.188, 95% CI: 1.219, 8.336], lack of formal education[AOR=9.405, 95%CI: 1.079, 81.943], lack of iron supplementation [AOR=3.189, 95%CI: 1.513, 6.720], WDDS <6 [AOR= 4.057, 95% CI: 2.157, 7.634], not taking additional meal (3+) [AOR=2.267, 95%CI: 1.211, 4.244], skipping meals [AOR=3.856, 95%CI: 1.099, 13.530) were significantly associated with under-nutrition. Conclusion and Recommendations: The present study revealed that there is a burden of suboptimal dietary practice and undernutrition among the studied participants. Predictors identified for suboptimal dietary practice were the family size and household food insecurity. Similarly, undernutrition was predicted by marital status, educational status, iron supplementation, additional meal intake, and meal skipping. Strategies should be designed at different levels by concerned bodies considering dietary practice and nutritional intake of pregnant women, with possible identified factors.