BackgroundPreterm birth (PTB) is a global issue although its burden is higher in low- and middle-income countries. This study examined the risk factors of PTB in Southeastern Terai, Nepal. MethodsIn this community-based cross-sectional study, a total of 305 mothers having children under the age of 6 months were selected using systematic random sampling. Data were collected by structured interviewer-administered questionnaires and maternal antenatal cards from study participants for some clinical information. Predictors of PTB were identified using multi-level logistic regression analysis at a P-value < 0.05. ResultsOf the total 305 mother-live-born baby pairs, 13.77% (42/305) had preterm childbirth. Maternal socio-demographic factors such as mothers from Dalit caste/ethnicity [adjusted odds ratio (AOR) = 12.16, 95% CI = 2.2-64.61] and Aadibasi/Janajati caste/ethnicity (AOR = 3.83, 95% CI = 1.01-14.65), family income in the first tercile (AOR = 6.82, 95% CI = 1.65-28.08), than their counterparts, were significantly positively associated with PTB. Likewise, other maternal and dietary factors, such as birth order first-second (AOR = 9.56, 95% CI = 1.74-52.53), and birth spacing <= 2 years (AOR = 5.16, 95% CI = 1.62-16.42), mothers who did not consume additional meal (AOR = 9.53, 95% CI = 2.13-42.55), milk and milk products (AOR = 6.44, 95% CI = 1.56-26.51) during pregnancy, having <4 antenatal (ANC) visits (AOR = 4.29, 95% CI = 1.25-14.67), did not have intake of recommended amount of iron and folic acid tablets (IFA) (<180 tablets) (AOR = 3.46, 95% CI = 1.03-11.58), and not having adequate rest and sleep (AOR = 4.83, 95% CI = 1.01-23.30) during pregnancy had higher odds of having PTB than their counterparts. ConclusionSome socio-demographic, maternal, and dietary behavior-related factors were independently associated with PTB. These factors should be considered while designing targeted health interventions in Nepal. In addition, we recommend specific measures such as promoting pregnant women to use available antenatal care and counseling services offered to them, as well as having an adequate diet to a level that meets their daily requirements.