The aerial parts of Nepeta teucriifolia Willd. were extracted with the solvents of different polarities. The antiproliferative activities of the extracts were evaluated against rat brain tumor (C6) and human cervix carcinoma (HeLa) cell lines. The phytochemical screening of the extracts was performed with TOF-LC/MS. The CH2Cl2 and EtOAc extracts showed considerable antiproliferative activities against HeLa cells at higher concentration (250 µg mL−1). The CH2Cl2 extract was found more active than the others on both cells. The phytochemical studies of the active extract led to the isolation of three new iridoids, teucriifolian A-C (1–3). The structure elucidations of the new compounds were performed using HPLC-TOF/MS, 1D and 2D NMR techniques. The compounds 1–3 were evaluated in terms of their antiproliferative activities against HeLa and C6 cells, respectively. The results indicated that only 2 had moderate antiproliferative activity against HeLa cells at 250 µg mL−1.