The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, "green" gypsum wallboard, and "green" carpet) under three relative humidity (RH) conditions (20%, 50% and 70% RH). A dynamic dualchamber test method was used. Results showed that a higher relative humidity led to a larger effective diffusion coefficient for both conventional wallboard and green wallboard. The partition coefficient (Kma) of formaldehyde in conventional wallboard was larger at 50% RH than at 20% RH, while the difference in Kma between 50% RH and 70% RH was insignificant. The partition coefficient of formaldehyde did not show significant change in green wallboard, but it increased slightly with the increase of relative humidity in carpet. The carpet was also found to be very permeable resulting in a diffusion coefficient at the same level as the formaldehyde diffusion coefficient in air. The data generated could be used to assess the sorption effects of formaldehyde on building materials and to evaluate its impact on the formaldehyde concentration in buildings.