We developed a modified staining technique using acridine orange to stain the nuclei of Rhizoctonia solani. Acridine orange solution was prepared in acetic acid buffer, pH 7.2. Staining for 15 min was critical for observing the nuclei. All of the isolates were found to be multinucleated. The nuclei appeared bright green with light orange background. This method is simple, rapid and reproducible.