Gp64 is a major envelope glycoprotein found in group I baculoviruses such as the multiple nucleopolyhedroviruses of Autographa californica. gp64 has been demonstrated to be responsible and sufficient for receptor binding, cell entry and low pH-triggered membrane fusion. Upon acidification in endosomes, gp64 undergoes a reversible conformational change which facilitates membrane fusion. Crystal structure of post-fusion conformation of gp64 has been solved previously. However, structures of the pre-fusion conformation and possible intermediates are still unknown. We have cloned, expressed and purified a polyhistidine-tagged soluble form of gp64 protein (gp64-his) to homogeneity using the baculovirus-insect cell expression system. We are investigating its structure and function with techniques including Small Angle X-ray Scattering (SAXS) in combination with on-line Size Exclusion Chromatography, and X-ray crystallography. Our recent solution X-ray scattering study of gp64 at the Australian Synchrotron yielded low resolution scattering data at both pre- and post-fusion pHs. Also, preliminary diffraction data of glycosylated form of gp64 crystals at pre-fusion pH has been collected at the Australia Synchrotron to 5 Å resolution.