The allelopathic effects of Artemisia lavandulaefolia were studied using several test plants and microbes. Aqueous extracts and volatile compounds of A. lavandulaefolia inhibited seed germination, seedling and root growth of the test species such as Achyranthes japonica. Lactuca sativa, Artemisia princeps var. orientalis. Oenothera odorata, Plantago asiatica. Aster yomena, Elsholtzia ciliata, and Raphanus sativus var. hortensis for. acanthiformis. The root growth of test species was more affected than shoot growth by allelochemicals of A. lavandulaefolia. Essential oil of A. lavandulaefolia had antibacterial and antifungal effects. However, the antimicrobial activity of the essential oil was dependent upon the microbial species and concentrations. Callus growth of Oryza sativa, Brassica campestris subsp. napus var. pekinensis and Achyranthes japonica was sensitive by the essential oil of A. lavandulaefolia. Twenty three chemicals were identified from A. lavandulaefolia essential oil by gas chromatography. Primary allelochemicals among them were 1, 8-cineole, 1-$alpha$-terpineol, $alpha$-terpinene. camphor, 2-buten-1-ol and azulene. We concluded that aqueous extract and essential oil of A. lavandulaefolia were responsible for allelopathic effects.