Formaldehyde (FA) is usually the most abundant air pollutant in the decorated residential buildings and also the most studied due to its potential role in allergic diseases and its carcinogenic properties. In the present work, according to Indoor Air Quality Standard (GB/T 18883-2002), a series of investigations were carried out at 83 decorative residences by Intescan 4160-19.99 formaldehyde detector in Changsha from November 2008 to October 2009. It is showed that formaldehyde pollution was very serious in decorated residences with a 100% occurrence in the specimens and mean concentrations of 0.11±0.07 mg/m3. Concentration of formaldehyde was ranging from 0.01 to 0.31 mg/m3 with 53.3% of the over the standard rate. The maxium level reached 4.5 times of the standard. The mean concentration of formaldehyde in different rooms was the following: Children room>bedroom (sanctum)>living room. Formaldehyde concentration in decorative residences was gradually on the decline with prolonged time. Indoor formaldehyde droped it concentration by 0.04 mg/m3seven months later. Therefore, the formaldehyde concentration in residential buildings was connected with the type of the room,decorated time, furnituring and other factors.