Bacillus thuringiensis var. kurstaki HD-1 (Dipel 25<), as a biological insecticide was tested against Spodoptera littoralis larvae infesting soybean plants either alone or combined with potassium carbonate as an adjuvant. The carbarnate chemical insecticide, lannate, was used for comparison. The materials were applied either through spraying or dusting. Results showed that potassium carbonate enhanced and significantly increased the effect of Dipel. Both techniques are suitable for use in control application. The recommendation of using a combination of Dipel at 250 gif and potassium carbonate (150 g/f) is advisable. This combination gave significant high larval reduction (96.86 % and 92.11 To) with an increase of 2.50 and 1.60 folds in yield after spraying and dust applications, respectively. The data also suggested that a combination of Dipel and potassium carbonate (Dipel K7CO3) may be an effective component of the future S. littoralis IPM programs on soybeans.