Postural stability while seated was investigated in 16 children with autism spectrum disorder (ASD) and 16 typically developed (TD) children, aged 7-8 years. The lateral and antero-posterior (A-P) deviations of the centre of pressure (COP) were serially measured during sequential, upper limb, desk-top tasks, including nine subtests. The average COP deviation was larger, especially in the lateral direction, in the group of children with ASD compared with TD children. However, the larger COP deviation in the children with ASD was not generalized across tasks. Analyses of subtests revealed that deviations were different on three and four (of eight) subtests in the lateral and A-P directions, respectively. The time needed to complete each subtest was not correlated with the lateral COP deviation but with A-P deviation during the subtest in the children with ASD. Preserved task performance with marked body sway in the children with ASD suggested that the body sway was not a functionally abnormal movement that disturbed performance but could be a compensatory movement to actually facilitate performance. A new approach with occupational therapy to support such compensatory movement of ASD children could be considered in their school life. Further studies, including those in the classroom, to clarify the relationship between daily task performance and body instability are necessary.