Hydrogen bonding in hard segment domains of segmented polyester polyurethaneurea (PUU) based on 4,4'-diphenylmethane diisocyanate (MDI), ethylene diamine (ED) and polybutylene adipate (PBA) (M.W.1,975 and M.W.1,228) was studied by means of IR spectroscopy. It was found that the double peak absorption of urea C=O groups occurred in the studied PUU with the increase of hard segment content. Two hydrogen bonding models of urea C=O groups in different hard segment sequence lengths of PUU were proposed. Three dimensional hydrogen bonding in hard segment domains can be formed by further bonding of the above planar hydrogen bondings.