The morphology of complex micellar assemblies is generally described using indirect methods such as small-angle X-ray scattering (SAXS) or small angle neutron scattering (SANS) that can yield to ambiguous descriptions of the nano-objects when the sample contains multiple structures or completely unknown structures. We herein propose to directly observe the nano-objects formed in P123 pluronic solutions (with and without rare-earth element-REE) using wet-Scanning Transmission Electron Microscopy (wet-STEM) and to compare the results with sample descriptions derived from SAXS and SANS measurements. The results obtained by the different analytical techniques are consistent. Each analytical method provides complementary information that allows the internal structure of the objects, their compositions and their mutual interactions to be described precisely. The main contributions of wet-STEM microscopy are to describe the nano-objects individually and, in particular, to show that the REE content can vary from 1 to 10 from one micelle to another, to observe the dynamics of the nano-objects in the liquid and to prove the coexistence of nano-objects with very different morphologies in the same system.