Disclosed is a method for improving the expression of Cry1A in plants that makes use of codons preferentially used in native plant genes. The coding sequence of the gene for the Bacillus thuringiensis delta endotoxin Cry1A crystal protein was analyzed and found to have codons not preferred by plants. By constructing a synthetic protein coding sequence that uses codons which are preferred in plant genes, expression of the protein in plant cells was improved.