Retinoblastoma (RB) is the most common malignant intraocular tumor in children. Fifty percent of RB patients are carriers of a predisposing germline mutation with high penetrance. RB1 has been identified as the only pathological gene. We present the rapid detection of an RB1 gene mutation in a Han pedigree of two RB patients from southern China. Total RNA was extracted from whole blood for reverse transcriptase-polymerase chain reaction (PCR) to analyze RB1 transcripts, and genomic DNA for PCR and direct sequencing to test RB1 exons. Allele-specific PCR was used to verify the mutation. The results showed that the bilaterally affected son and the unilaterally affected father were both heterozygous for the nonsense mutation c.1363C>T (p.R455X) in exon 14 of RB1. Our studies suggest the molecular basis of RB in this Chinese family and provide further evidence that codon 455 is one of the recurrent spots for mutations in RB1.