Human inhibitor 1 is a heat- and acid- stable phosphor-protein, which regulates a diversity of cellular processes through the inhibition of protein phosphatase 1 (PP1). After phosphorylation of Thr35 by protein kinase A, human inhibitor 1 is converted into a potent inhibitor of protein phosphatase 1. In order to gain insight to the interaction between inhibitor-1 and PP1, we have used multidimensional heteronuclear NMR techniques to elucidate the structural properties of inhibitor-1. We have assigned full resonances of inhibitor 1. The secondary short helices spanning from 24- 28, 81-86, 103-109, and 127-131. These structural data can provide as a model to predict the interaction of protein phosphatase and its endogeneous inhibitor proteins.