Dietary diversification is a sustainable and appealing strategy for pregnant women to ensure a balanced dietary intake. In Ethiopia, despite the implementation of various nutritional initiatives, inadequate dietary diversity remains a significant factor contributing to adverse birth outcomes. Thus, this study aimed to assess the dietary diversity and associated characteristics among pregnant women attending antenatal care in Eastern Ethiopia. Institution-based cross-sectional study was conducted from April 28 to May 28, 2021. A total of 420 pregnant women were selected using a systematic random sampling technique. We used the adjusted odds ratio (AOR) and a 95% confidence interval to estimate the strength of the association. We used a p-value of 0.05 to declare statistical significance. Only 35.0% (95% CI: 30.5, 39.5) of the 420 pregnant women involved in this study received appropriate dietary diversity. Having an educational level of college and above (AOR 3.01, 95% CI: 1.19–7.5), being an urban dweller (AOR = 3.57, 95% CI: 1.68–7.52), eating three meals and above (AOR = 7.62, 95% CI: 2.88–9.03), and having ≤4 family sizes (AOR = 9.33, 95% CI: 4.06–10.4) were significantly associated with an adequate dietary diversity score among pregnant women. This study found that pregnant women had inadequate overall consumption of a diversified diet. Increasing meal frequency, enhancing women’s education, raising awareness of dietary diversity among rural inhabitants, and offering counselling on family planning utilisation during ANC services are all beneficial in promoting dietary diversity among pregnant women.