Tumor Necrosis Factor (TNF) are expressed in milk. Experimental data indicate enhanced brain growth and cognitive development in the mouse offspring given milk deficient in TNF and TNF-dependent chemokines. Although monoclonal antibodies against TNF (TNFmAb) are used during breastfeeding due to minimal milk excretion, whether it affects endogenous TNF levels in human milk is unclear. A prospective cohort study was conducted in 26 breastfeeding women with inflammatory bowel disease (IBD) and 31 non-IBD women. Milk TNF and related chemokines were measured at 5-6 weeks postpartum (early-lactation point) as a primary endpoint and further determined at 13-14 weeks postpartum. In a subset of their infants, neurocognitive development was assessed at 12 and 18 months of age using Bayley-III tool. While milk TNF levels were not significantly different between the control and those with IBD, women with IBD receiving TNFmAb showed 70% lower median milk TNF than those without TNFmAb (P = 0.019) at early lactation period. TNF-dependent chemokines (MIP-1β and IP-10) also showed similar patterns. Neurocognitive development of the infants was not significantly different among the groups. Women with IBD receiving TNFmAb show significantly lower milk TNF/chemokines at 5-6 weeks postpartum than those without TNFmAb. gov NCT03397108. We found that milk concentrations of Tumor Necrosis Factor (TNF) and TNF-dependent chemokines (MIP-1β and IP-10) are low in women with inflammatory bowel disease who are receiving anti-TNF monoclonal antibody (TNFmAb), compared to those without concurrent anti TNF therapy. While maternal use of TNFmAb during breastfeeding is considered inconsequential to infant health due to their low levels of milk excretion, it affects profiles of endogenous cytokines in milk. Our findings provide a rationale to investigate human implications of the animal data in the literature that suggest enhancement of neurocognitive development of the offspring fed with milk deficient in TNF-dependent chemokines.