We present the data corresponding to the ultrastructural characteristics of Paenibacillus polymyxa isolates and control efficacy of P. polymyxa ShX301 for controlling Verticillium wilt of cotton, isolated in experimental fields at the Sanyuan Agricultural Experiment Station of North-West Agriculture and Forestry University, Sanyuan county, Shaanxi province, China. Ultrastructural characteristics of P. polymyxa isolates made using technique of transmission electron microscopy. A strain ShX301 has a broad-spectrum antifungal activity against V. dahliae and other plant pathogens and has been used for in vitro experiments for controlling this disease in greenhouse, "Biocontrol potential of Paenibacillus polymyxa against Verticillium dahliae infecting cotton plants" [1].