Fishâmint ( Houttuynia cordata Thunb .), belonging to family Saururaceae, has long been used as food and traditional herbal medicine. The present study was framed to assess the changes occurring in the essentialâoil composition of H. cordata during annual growth and to evaluate allelopathic, antibacterial, antifungal, and antiacetylcholinesterase activities. The essentialâoil content ranged from 0.06 â 0.14% and 0.08 â 0.16% in aerial parts and underground stem, respectively. The essential oils were analysed by GC â FID , GC / MS , and NMR ( 1 H and 13 C). Major constituents of aerialâparts oil was 2âundecanone (19.4 â 56.3%), myrcene (2.6 â 44.3%), ethyl decanoate (0.0 â 10.6%), ethyl dodecanoate (1.1 â 8.6%), 2âtridecanone (0.5 â 8.3%), and decanal (1.1 â 6.9%). However, major constituents of undergroundâstem oil were 2âundecanone (29.5 â 42.3%), myrcene (14.4 â 20.8%), sabinene (6.0 â 11.1%), 2âtridecanone (1.8 â 10.5%), Î² âpinene (5.3 â 10.0%), and ethyl dodecanoate (0.8 â 7.3%). Cluster analysis revealed that essentialâoil composition varied substantially due to the plant parts and season of collection. The oils exhibited significant allelopathic (inhibition: 77.8 â 88.8%; LD 50 : 2.45 â 3.05 Î¼l/plate), antibacterial ( MIC : 0.52 â 2.08 Î¼l/ml; MBC : bacteriostatic) and antifungal ( MIC : 2.08 â 33.33 Î¼l/ml; MFC : 4.16 â 33.33 Î¼l/ml) activities. The results indicate that the essential oil from H . cordata has a significant potential to allow future exploration and exploitation as a natural antimicrobial and allelopathic agent.