We have isolated migrastatin, an inhibitor of tumor cell migration, from a cultured broth of Streptomyces sp. MK929-43F1. In this paper, we describe the physico-chemical properties (summarized in Table 1) and structure elucidation of migrastatin. The molecular formula was established as C27H39NO7 by HRFAB-MS. Using ¹H and ¹³C NMR, DEPT, HMQC, ¹H COSY, HMBC, HOHAHA, and NOESY spectra, we established a 14-membered lactone ring for the C1-C13 unit, determined the side chain to contain a symmetrical glutarimide structure, revealed the E configurations for the olefins at C-2 and C-6 (via spin coupling constants J2-3=15.7 Hz and J6-7=15.5 Hz) and Z configuration for the trisubstituted olefin (via NOE between 11-H and 23-H in the NOESY spectrum), and finally determined the structure of migrastatin. The absolute stereochemistry of migrastatin is now in progress.