AbstractSoy-based adhesive’s sensitivity to microbial attack is an aspect that restricts its future application. In an attempt to combat microbial attacks, several preservatives have been evaluated to determine their effects on mold resistance. In this paper, the inhibitory effect of p-cumylphenol was investigated by observing mold growth on modified soybean-flour adhesives and by evaluating the bonding strength and surface mold growth of bonded poplar plywood. Visual images, scanning electron microscopy, and tensile testing were used. The results showed that the initial microbial attack was delayed and the degree of attack was alleviated because of the preservatives. The bonding strength decreased in samples that contained p-cumylphenol after the samples were exposed to high humidity. Additionally, no correlation was observed between the degree of microbial growth on the surface of the plywood and amount of the preservatives. These results revealed that it was feasible to incorporate p-cumylphenol into soy-based adhesives as glue line treatment to improve the mold resistance. Finally, surface treatment of the veneer should be taken into consideration during the plywood manufacturing.