NMR is one of the most powerful tools to determine protein structure, function, and its biding interface in solution. In structural genomics studies, the solubility and purification of overproduced proteins are serious problems. Here we succeeded the NMR analysis of a glutathione-S-transferase (GST) tagged small protein, ubiquitin, without removing tag, which enables the easier purification and the higher solubility of proteins. The ¹H-¹⁵N HSQC spectra of GST-tagged human ubiquitin were measured in solution and also on the glutathione sepharose column resin where the target protein was immobilized. The measured two spectra were different in linewidth, however, quite similar in resonance position. Site specific interaction with yeast ubiquitin hydrolase was not inhibited by the GST-tagging as well as the immobilization on resin. These results indicated that the ubiquitin portion of GST-ubiquitin retained the same conformation as the isolated ubiquitin, and that its motion was independent of that of GST. This technique will be applicable for hardly soluble proteins that tend to form aggregates, such as membrane protein.