The crystal structure of natural rubber has been studied by many researchers including Bunn and Nyburg. However, the accepted crystal structure has not been reported. In the present study, the X-ray crystal structure analysis was carried out by using an imaging plate at -50 degreesC. Four molecular chains with ST (S) over bar cis (S) over bar TScis conformation pass through a unit cell with a = 12.41 Angstrom, b = 8.81 Angstrom, c = 8.23 Angstrom, beta = 94.6degrees, and P2(1)/a-C-2h(5). In the crystal lattices, two molecular chains related by the mirror symmetry statistically occupy a crystal site with the ratio 0.67:0.33.