Background: Intellectual disability (ID) accounts for 70% of all disabilities among children in China's Second National Sampling Survey on Disability. Although studies have shown a relationship between social class and ID in children, none have investigated the association of socioeconomic variables in Chinese children with mild or severe ID. Methods: Data for children aged 0-6 years with and without ID were abstracted from the Second National Sampling Survey on Disability in China, conducted in 2006. Crude odds ratios showed the effect of sociodemographic factors on mild and severe ID. Adjusted odds ratios (OR[subscript a]) (95% confidence intervals) estimated the independent effects of these factors. Results: For both mild and severe ID, risk of having ID increased with male sex, birth to a woman aged 35 years and older, lower maternal education, mother's older age at delivery, lower income and rural residence. After age, gender and parent disability were controlled, mothers aged 35 years and older were more likely to have a child with ID: mild ID, OR[subscript a] 1.47 (1.15-1.88); severe ID, OR[subscript a] 1.32 (1.00-1.73). There was an approximate increasing monotonic risk of severe ID with increasing socioeconomic disadvantage: lowest income, OR[subscript a] 3.00 (2.19-4.12); low income, OR[subscript a] 2.28 (1.63-3.19); lower middle income, OR[subscript a] 1.72 (1.27-2.33); middle income, OR[subscript a] 1.73 (1.28-2.36). Conclusions: There is a significant relationship between sociodemographic factors and ID. Similar patterns were found for both mild and severe ID. Recommendations are given for preventing ID in Chinese children.