In situ synchrotron X-ray diffraction measurement of solid C-60 under high pressure up to about 26 GPa was performed using He gas as pressure transmitting medium. This is the first study to precisely investigate the structural property of the He intercalated C-60 under high pressure in a few tens GPa range. It was found that the He intercalated C-60 solid is much less compressible than the pure C-60 solid. The bulk modulus of the He intercalated C-60 solid is determined to be 35.1 (6.0) GPa. The effect of hydrostaticity on the deformations of unit cell and C-60 molecule is also discussed. (C) 2007 Published by Elsevier B.V.