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The Japanese beetle, Popillia japonica, is a minor pest in Japan but has become a serious invasive species in several parts of the world, causing damage in a variety of crops and high costs for its control. Many different methods of control have already been applied, including chemical and cultural measures, as well as mass-trapping. The efficacy of biological control attempts, using parasitoids, nematodes, fungi, or bacteria has also been discussed especially with regard to added value of lower ecological impact. The effect of Bacillus thuringiensis (Bt) treatments is usually attributable to the proteins accumulated in the parasporal body of the bacteria. In this context, a study was conducted to assess the insecticidal activity against P. japonica of the Bt 3-domain non-parasporal body accumulated Cry1Ia protein, and the structurally distant Bt proteins Mpp23Aa and Xpp37Aa. Their activity was tested against P. japonica larvae using a leaf-dip protocol, and only the Cry1Ia showed some activity. The results suggest that additional studies on Bacillus proteins are needed for developing new biological control strategies against P. japonica.