We aimed to determine the in vitro and in vivo synergistic antiallergic effect of guaijaverin and epigallocatechin gallate (EGCG) complex (GEC), and the antiallergic rhinitis (AR) properties of guaijaverin-rich Psidium guajava and EGCG-rich Camellia sinensis (ILS-F-2301). GEC showed synergistic inhibition of beta-hexosaminidase by 4.20% and interleukin (IL)-4, -5, and -13 by 4.08%, 0.67%, and 4.71%, respectively, while increasing interferon (IFN)-gamma by 12.43%, compared with EGCG only. In addition, 50 mu g/mL of ILS-F-2301 inhibited beta-hexosaminidase release, and inhibited IL-4, -5, and -13 by 61.54%, 58.79%, and 59.25%, respectively, while increasing IFN-gamma (showing 133.14% activation). Moreover, 50 mu g/mL of ILS-F-2301 suppressed p-STAT6 and GATA3, while p-STAT1 and T-bet increased, and 0.039 mu g/mL of guaijaverin or 5.275 mu g/mL of EGCG modulated T helper (Th)1- and Th2-related proteins. These data suggested that guaijaverin and EGCG in ILS-F-2301 was the main active compound involved in Th1/Th2 modulation. In the AR mouse model, the administration of ILS-F-2301 inhibited ovalbumin (OVA)-specific IgE, histamine in serum; it also inhibited IL-4 and -5 by 28.23% and 47.15%, respectively, while increasing IFN-gamma (showing 37.11% activation), compared with OVA/Alu-treated mice. Taken together, our findings suggest that ILS-F-2301 is a functional food for alleviating anti-AR.