The line observations of high angular resolution H₂CO 218 GHz were investigated in low-mass protostars IRAS 16293-2422 and L1448-C. There was excess unresolved compact emission centered for both sources which occurred due to accretion disks <200AU in size. The constant H₂CO abundance throughout the envelope cannot fit interferometer data of two H₂CO lines simultaneously on longest and shortest baselines. H₂CO abundance drops in cold dense part provides good fits to single-dish and interferometer data on short baselines for both sources.