We have recently been able to form a thin graphene oxide (GO) film with uniform thickness around 30±2Å from aqueous GO suspensions by spin coating (onto small wafers for ellipsometry and large silicon blocks for neutron reflection). The films have high stability under liquid flush (pure water, THF and 5% Decon) and can thus be used for further physical studies under liquid/solid condition. The aim of this proposal is to make the first NR measurements of the structure and composition of the GO films and validate the fittings from spectroscopic ellipsometry.