Objective:To study the variation of formaldehyde concentrations in indoor air of newly decorated.Methods:54 families and 52 public places with indoor decoration were selected to be monitored in different stages.Results:The over standard rate for the air formaldehyde sample was from 79.9% to 85.4% during one year after the tenements were decorated.50.0% during the period from the first year to the next year and the over standard rate for the air formaldehyde sample was18.3% after the tenements were decorated for two years.There was significant difference in the rate among three different periods (P0.05).The over standard rate for the air formaldehyde sample was from 65.5% to 81.3% within 6 months after the public places were decorated.36.84% during the period from the 7th month to the 12th month and the over standard rate for the air formaldehyde sample was lower than 15.4% after the public places were decorated for one year.There was significant difference in the rate among three different periods (P0.05).Conclusion:During the course of monitoring formaldehyde concentrations in indoor decreased apparently with the prolongation of the duration after the end of the decoration.The formaldehyde concentrations did not reach the standard until the tenements were decorated for two years and the formaldehyde concentrations reached the standard after the public places were decorated for one year.