Leveraging bioactive compounds with immunomodulatory effects to boost immune functions represents a promising strategy for therapeutic intervention. The main objective of this work was to investigate the influence of the partial acid hydrolysis of an arabinoxylan extracted from Plantago ciliata Desf. seeds into oligosaccharides on its immunomodulatory effect. The resulting oligosaccharides and their polymer were evaluated for their potential to improve the phagocytic capacity (PC) and the phagocytic activity (PA) of polymorphonuclear neutrophils (PMNs) through the uptake of Candida albicans and to moderate alternative complement pathway (ACP) activation. As a result, the arabinoxylan derived from P. ciliata seeds (AXPCs) and its oligosaccharides (AXOPCs) significantly enhanced the PC of PMN cells, with EC50 values of 0.14±0.23 and 0.12±0.10 mg/mL, respectively. Zymosan used as a reference exhibited the highest PC with an EC50 0.07±0.08 mg/mL. However, for PA, zymosan still demonstrated the highest activity with an EC50 of 0.22±0.46 mg/mL compared to 0.33±1.36 and 0.30±0.74 mg/mL for AXPCs and AXOPCs, respectively. Moreover, AXPCs and AXOPCs were tested as moderator inhibitors of the complement system, showing maximum inhibition percentages of 40.11±8.38% and 50.57±10.45% at 1 mg/mL, with IC50 values of 1.49±0.40 and 1.02±0.20 mg/mL, respectively, compared to 61.52±7.17% and 70.89±5.78% for heparin used as a reference. These results suggest that AXPCs and AXOPCs can serve as relevant therapeutic immunomodulatory factors.