Rubinstein-Taybi syndrome (RTS), also known as 'broad thumbs syndrome' or 'broad thumb-hallux syndrome', is a malformation syndrome characterized by the triad of broad thumbs or first toes, a peculiar facial expression called 'comical face' and mental retardation. Although various malformations are combined with the triad, polydactyly is rare. We treated a male patient with RTS complicated by postaxial polydactyly of the foot. His clinical course was different from typical patients with polydactyly, especially in the aspect of walking development. Osteoplasty-combined surgery, which was ideal for anatomical reconstruction, was performed on the patient at 2 years and 11 months of age. A 4-year follow-up period was required until there was an improvement of dysbasia.