The aim of the study was to investigate how maternal dietary patterns and maternal/fetal cytokines are associated with birth weight and whether cytokines mediate the association. A total of 469 pregnant women and their children were recruited for this prospective study. Dietary patterns in pregnancy were identified using factor analysis of data from three consecutive 24 h dietary recalls. Maternal and umbilical blood serum cytokines (adiponectin (APN), IL-6 and interferon-γ) were measured via ELISA. Path analysis was used to explore the relationships between maternal diet, cytokines and birth weight. Four dietary patterns were identified: a mainly fruit, dairy products and poultry diet (FDP); a mainly vegetables, beans and pork diet (VBP); a mainly fish, shrimp and soup diet (FS) and a mainly tuber and egg diet (TE). Path analysis showed the order of effects of dietary patterns on birth weight was FS>FDP>TE>VBP (β=0·130, 0·109, –0·094 and 0·046, respectively). Only the TE pattern’s effect was negative. Maternal and fetal APN were positively associated with birth weight (β=0·045 and 0·226, respectively), and they mediated the association between the TE pattern and birth weight (indirect effect was 5·3 %). Maternal IL-6 was negatively associated with birth weight (β=–0·067) and mediated the association between maternal FDP and VBP patterns and birth weight (indirect effects were 10·1 and 100·0 %, respectively). All variables in the path explained 33·6 % of variation. These results suggested that maternal dietary patterns in pregnancy are associated with birth weight and mediated directly and indirectly through some maternal/fetal serum cytokines.