Preterm birth is the leading cause of perinatal mortality and morbidity. Some prospective cohort studies suggested that fish and shellfish consumption may affect the incidence of preterm birth. However, conflicting evidence exists on the relationship between fish and shellfish consumption and preterm birth. A total of 10 179 women from Gansu province were interviewed after delivery to collect information on their past intake of fish and shellfish using FFQ. Logistic regression models were used to estimate OR and 95 % CI to examine the association between fish and shellfish consumption and preterm birth and its clinical subtypes. Fish and shellfish consumption was associated with reduced risk of preterm birth (OR = 0·65, 95 % CI 0·56, 0·77). Increasing frequency of fish and shellfish consumption, compared with no fish and shellfish consumption, was associated with decreasing odds of preterm birth. Besides, increasing weekly total amount of fish and shellfish consumption, compared with no fish and shellfish consumption, was also associated with decreasing odds of preterm birth. Significant trend effect was also seen between fish and shellfish consumption and very preterm birth (P for trend = 0·001) and spontaneous preterm birth (P for trend = 0·003). Interaction was observed between total fish and shellfish consumption with maternal age (P for interaction = 0·041) and pre-pregnancy BMI underweight (P for interaction = 0·012). Our findings showed that maternal fish and shellfish consumption was associated with lower incidence of preterm birth.We recommend for the national guideline of ≥350 g/week of fish and shellfish consumption among pregnant women.