Adsorption is widely regarded as the most promising method for uranium extraction. Among the various materials that have been studied, graphene oxide (GO) has attracted intensive interest because of its large specific surface area and abundant oxygen-containing functional groups. However, the layers tend to aggregate owing to pronounced Van der Waals forces, which reduce the surface area and diminish the likelihood of contact between uranyl ions and adsorption sites. Graphite oxide is an intermediate product of GO, with a simple preparation process and low cost. In this study, graphite oxide nanosheets (GONs) were synthesized using graphite oxide powder as the raw material and the NaOH activation method. GONs possessed a larger specific surface area and more carboxyl groups, which resulted in an excellent uranium adsorption capacity. The maximum adsorption capacity was found to be 578.0 mg·g−1, and the adsorption rate was 90.8% within 30 min. The adsorption process closely resembled the pseudo-second-order model and the Langmuir model. The mechanism of uranium adsorption by GONs was the synergistic coordination of -COOH and -OH with U(VI). This research suggests that the novel uranium adsorbent GONs can be applied to efficiently capture U(VI) from radioactive wastewater.