An in vitro bioassay-guide revealed that the methanol (MeOH) extract of the whole plant of Patrinia saniculaefolia (Valerianaceae) showed cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) dual inhibitory activity by assessing their effects on the production of prostaglandin $D_2$ ($PGD_2$) and leukotriene $C_4$ ($LTC_4$) in mouse bone marrow-derived mast cells (BMMCs). Phytochemical study of the MeOH extract of this plant led to the isolation of twelve compounds; ${eta}$-farnesene (1), squalene (2), nardostachin (3), patridoid I (4), patridoid II (5), patridoid II-A (6), oleanolic acid (7), oleanonic acid (8), 23-hydroxyursolic acid (9), oleanolic acid 3-O-${alpha}$-L-arabinopyranoside (10), oleanolic acid 3-O-${eta}$-D-glucopyranoside (11), oleanolic acid 3-O-[${eta}$-D-xylopyranosyl-(1${ ightarrow}$3)-${eta}$-D-(6-O-butyl)glucuronopyranoside] (12). Among the compounds, 4 and 5 strongly inhibited both the COX-2-dependent $PGD_2$ generation with $IC_{50}$ values of 8.7 and 13.6 ${mu}M$, respectively, and the generation of $LTC_4$ in the 5-LOX dependent phase with $IC_{50}$ values of 41.7 and 46.9 ${mu}M$, respectively, which suggest that the anti-inflammatory activity of P. saniculaefolia might occur in part via the inhibition of both $PGD_2$ and $LTC_4$ generation by 4 and 5.