The roots and rhizomes of licorice ( Glycyrrhia ) species have been used extensively as natural sweeteners and herbal medicines. The aim of this work was to determine the in vitro anti-inflammatory effects of glycyrrhizic acid (GA) and 18β-glycyrrhetinic acid (18βGA) from licorice in a lipopolysaccharide (LPS)-stimulated macrophage model. The results showed that treatment with 25-75 μM GA or 18βGA did not reduce RAW 264.7 cell viability but did significantly inhibit the production of LPS-induced nitric oxide (NO), prostaglandin E(2) (PGE(2)), and intracellular reactive oxygen species (ROS). Western blotting and reverse transcriptase polymerase chain reaction (RT-PCR) analyses revealed that GA and 18βGA significantly reduced the protein and mRNA levels of iNOS and COX-2 in LPS-induced macrophages. Both GA and 18βGA inhibited the activation of NF-κB and the activities of phosphoinositide-3-kinase (PI3K) p110δ and p110γ isoforms and then reduced the production of LPS-induced tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-1β in a dose-dependent manner. In conclusion, these results indicate that GA and 18βGA may provide an anti-inflammatory effect by attenuating the generation of excessive NO, PGE(2), and ROS and by suppressing the expression of pro-inflammatory genes through the inhibition of NF-κB and PI3K activity. Thus, the results suggest that GA and 18βGA might serve as potential agents for the treatment of inflammatory-mediated diseases.