Greenhouse and field experiments were conducted in 2013/2014 and 2014/2015 to study the effect of Bacillus subtilis, when applied as soil treatment in combination with concentrations of essential plant oils as dipping treatment on onion white rot infection. Oils of cumin, cardamom and thyme were tested at five concentrations (0.25%, 0.50%, 1%, 2%, and 4%), on the linear growth of Sclerotium cepivorum isolates. Cumin oil had the strongest inhibitory effect on linear growth followed by thyme. Reduction in linear growth increased by increasing concentration of the tested plant oil. Under artificial and natural infection conditions in greenhouse and field trials, B. subtilis combined with different concentrations of essential plant oils were significantly effective in reducing incidence of onion white rot, compared with untreated control. Also, treatments increased fresh and dry weight under greenhouse conditions as well as increased onion bulb yield in field trials. Generally, cumin oils followed by thyme with B. subtilis gave the highest percentage of apparent healthy plants as well as the highest efficacy in reducing onion white rots compared to other treatments except fungicides treatment (Trust EW 25). The superior treatments were obtained by cumin at 2% with B. subtilis and it was the nearest treatment to fungicides in reducing of onion white rots incidence.