Machado-Joseph disease (MJD)/spinocerebellar ataxia type 3 (SCA3) is caused by unstable CAG trinucleotide repeat expansion in the coding region of the MJD gene. In this study, we describe a non-radioactive polymerase chain reaction (PCR) method to detect the CAG repeat range of the MJD gene. This technique allows direct visualization of the PCR products on ethidium bromide-stained agarose gels within hours. In this study, genomic DNA samples isolated from peripheral lymphocytes, amniotic fluid cells, and chorionic villi were tested with two sets of commonly used MJD primers. PCR conditions were optimized, which resulted in clear visualization of both the primer sets on 3% agarose gels. Ten out of 25 candidate MJD patients have been identified with this method to date, with no false-positive or false-negative diagnoses. This simple, reliable, and cost-effective method can be used for patient diagnosis, pre-symptomatic diagnosis, and prenatal diagnosis.