To evaluate the associations of socioeconomic class (middle and lower) with sleep behaviour, two public and two private primary schools were randomly selected in three district areas (out of seven) in Macao, China. The sleep behaviour of these children (primary grades one to six) was examined with a validated, locally developed questionnaire. In all, 756(83.3%) of the 908 questionnaires were completed and returned, 330(43.7%) for girls and 426(56.3%) for boys. Only 142(19.9%) children reached the recommended standard of 10 hours of daily sleep on weekdays that were not during an exam period. Thus, 571(80.1%) did not get the required sleep (x 2 = 9.748; degrees of freedom [df] = 1; P = 0.002). The situation was even worse in exam periods during weekdays, with 626 (87.6%; x 2 = 19.406; df = 1; P = 0.000) children not obtaining 10 hours of sleep during that time. These results show that improper sleep behaviour in Macao children is associated with stressed school workload, bedtime difficulty, and environmental factors. Early intervention on these factors might help the children to establish adequate sleep habits.