This study was conducted to investigate biocontrol potential of Paenibacillus ehimensis KWN38 against Fusarium oxysporum f.sp. lycopersici causing Fusarium wilt disease in tomato. Our result showed that P. ehimensis KWN38 produced extracellular organic compounds and crude enzyme to inhibit F. oxysporum f.sp. lycopersici conidial germination in in vitro assays. Tomato seedlings were treated with water (W), grass medium (G), G with P. ehimensis KWN38 inoculation (GP) and G along with synthetic fungicide (GSf). Disease symptoms were was first observed in G and W at 12 days after infection (DAI) while symptoms were noticeable in the GP and GSf treatments at 20 and 24 DAI, respectively. Tomato plants treated with P. ehimensis KWN38 or fungicide significantly reduced Fusarium wilt disease incidence and severity as compared to control tomato plants treated with water and grass medium. The similar results were also found in the root mortality of tomato plants. At 25 DAI, most plants in control treatments (W and G) wilted and the brown vascular systems of infected plants was clearly differentiable from normal green vascular system of healthy plants from GP and GSf. Plants in the GP showed higher fresh and dry weights of both root and shoots than those in W and G treatments. Leaf peroxidase and polyphenol oxidase activities of tomato plants in G and W were higher than those in GP and GSf. Root enzyme activities showed a similar pattern but the values were higher than leaf enzyme. The results clearly demonstrated that P. ehimensis KWN38 may be considered as biocontrol agent of Fusarium wilt disease in tomato.