Recent genetic studies for osteoarthritis (OA) have been focused on ASPN, the gene encoding asporin, where aspartic acid (D)-repeat polymorphisms are associated with OA in several ethnic groups. The purpose of the present study is to further examine the association of the D-repeat polymorphism in a Han Chinese population. The D-repeat polymorphism was genotyped in 354 knee OA patients (257 women and 97 men) who suffered from primary symptomatic knee OA with radiographic confirmation, and the association of the repeat with various clinical parameters was examined. The age at onset (years) in patients with the D14 allele (mean: 51.9, SD: 8.5) was younger than that those without the D14 allele (mean: 54.9, SD: 10.9) (P = 0.023). Survival analysis showed D14 was significantly associated with age at onset of OA (P = 0.004 in the dominant model). The average age at onset of patients with the D13/D13 genotype (mean: 56.1, SD: 11.1) was older than those without the D13/D13 genotype (mean: 53.0, SD: 9.9) (P = 0.013). Our study further highlighted the significance of asporin in OA.