Used alkaline-phosphatase-labeled DNA as a probe to examine the expression of foreign UidA gene in transgenic plants. Alkaline phosphatase coupled with polyethyleneimine (PEI) using P-benzoquine as the cross-linking reagent was covalently linked to single-stranded DNA via glutraldehyde. Such DNA-enzyme complexes were used as a probe for dot hybridization and Southern blot. After hybridization and incubation with a substrate solution, results can be observed directly in three to six hours and the results showed that it was a sensitive, specific, rapid, safe and economical probe. Dot hybridization analysis showed that the UidA gene was transformed into the target plants and southern blot showed that there were at least 5 copies of UidA gene in transgenic plants.