The effect of amaranth peptides on the activity and expression of tissue factor (TF) on THP-1 activated cells was evaluated in vitro. An active anticoagulant peptide fraction (AF) was found to inhibit TF expression (IC50 = 0.39 mg mL-1) and activity. Immunocytochemical fluorescence confocal microscopy analysis showed that treated monocytes decreased TF membrane translocation by 49.0% and increased two-fold in nuclei compared to a positive control, indicating a decrease of active TF to initiate the coagulation cascade. Moreover, a cytokine array suggested that the AF mechanism of action implied the inhibition of the NF-κB pathway. Expression of MIP-3α, interleukin-1β, interleukin-1α, TARC, pentaxin 3, and PDGF-AA cytokines was highly suppressed by AF peptides, producing reductions of 78.8%, 61.8%, 54.1%, 42.6%, 37.9% and 37.8%, respectively, compared to a positive control. The results suggest a potential mechanism for the antithrombotic and anti-inflammatory effect of AF, by showing that amaranth peptides play a negative feedback regulatory role over the NF-κB pathway. In this research, we link for the first time the immunomodulatory activity of amaranth peptides with the inhibition of TF expression and therefore their antithrombotic potential.