Soil or seed applications of plant growth-promoting rhizobacteria (PGPR) have been used to enhance growth of several crops as well as to suppress the growth of plant pathogens. In this study, we selected a PGPR strain, Paenibacillus polymyxa strain E681, out of 3,197 heat-stable bacterial isolates from winter wheat and barley roots. Strain E681 inhibited growth of a broad spectrum plant pathogenic fungi in vitro, and treatment of cucumber seed with E681 reduced incidence of damping-off disease caused by Pythium ultimum, Rhizoctonia solani, or Fusarium oxysporum. When inoculated onto seeds as vegetative cells or as endospores, E681 colonized whole cucumber root systems and root tips. Different temperatures such as $20^{circ}C;and;30^{circ}C$ did not affect root colonization by strain E681. This colonization was associated with a consistent increase in foliar growth of cucumber in the greenhouse. These results indicate that strain E681 is a promising PGPR strain for application to agricultural systems, particularly during the winter season.