Abstract: The collocated data from quasi-synchronous Aqua/MODIS and CloudSat/CPR measurements during 2008 were used to investigate the spatial distributions and vertical structures of multilevel warm cloud systems over global oceans. By modifying the traditionally warm cloud determination scheme that is based singly on cloud top temperature criterion, it is found that most oceanic warm-cloud units are of three dominant structures, including single-layer warm cloud, double-layer semi-warm cloud and double-layer warm cloud. The statistical results show that on the global scale, single-layer warm cloud (SWC), double-layer semi-warm cloud (DSC) and double-layer warm cloud (DWC) account for 77.14%, 19.15% and 3.71%, respectively. In the global distribution, the difference between the three configurations of warm clouds is obvious, especially at the geolocation with frequent occurrences. In terms of structural parameters such as cloud top height, cloud base height and cloud thickness, the statistical characteristics of the lower warm cloud in DSC are very close to that of SWC, showing the similarity of the two kinds of warm clouds on the geometric structure. This indicates that the upper cold cloud in DSC does not cause changes in the lower warm cloud, and the upper and the lower clouds may have originated from independent cloud-formation processes. The structure of the upper warm cloud in the DWC configuration is obviously different from that in the SWC, while the lower one is close to that of SWC, but with smaller cloud top height and cloud thickness. In addition, the thinner the lower warm cloud, the stronger the upper warm cloud can develop upward. These results suggest that there is probably a relevance between the upper and lower warm clouds in DWC, and these two cloud layers are closely correlated during their evolution.