Recognition is a central event in a variety of biological phenomena and the first step in numerous processes based on cell-cell interactions. As the most external part of the cell, cell wall mediates the initial physical and chemical interaction between microorganisms and the environment, including the host. Proteins have been implicated in most of cell wall functions. Recent research has been limited primarily to the function of proteins as adhesions, and results showed such recognition may be mediated by lectin. In recent studies, great attention has been paid to interaction between mycoparasites and mycohost. Olpitrichum tenellum is a biotrophic contact mycoparasites, and Alternaria alternata is one of its host fungi. The recognition mechanism between them was by far not reported. This research focused on the purification, properties and adhesion activity of a lectin from A. alternata in order to reveal the recognition mechanism between mycoparasite and mycohost, also to provide basis for further research. A lectin from isolated A. alternata cell walls was purified to SDS-PAGE homogeneity by ammonium sulphate fraction, DEAE-Sepharose Fast Flow chromatography and Sephacryl S-100 chromatography. The lectin, named AAL, was a glycoprotein with an apparent molecular weight 37.2 kDa by gel filtraction. AAL may be a cell recognition molecule which mediates the adhesion of O. tenellum cells to A. alternata cells. Adhesion experiments between AAL and conidia of O. tenellum , >90% conidia adhered within 30 min at concentrations as low as 3.325 µg ml^-1. Compared to adhesion in the absence of AAL, there was no significant effect on spore adhesion.