The main target in this study was to increase adhesion of unsaturated polyester (UP) adhesive to aluminum substrates by structuring the aluminum surface on the microscale and nanoscale as well as by functionalizing the surface with 3-methacryloxypropyltrimethoxysilane. The micrometer-level surface structures were produced with a micro-mesh printing technique and sandblasting, while a nanoscale pseudoboehmite surface structure was obtained with a boiling water treatment. These modifications were combined to form different hierarchical surface structures on the aluminum substrate. The adhesion strength of polyester to aluminum was assessed with a tensile-shear test. The mere micro-mesh printed pattern increased the tensile-shear strength of the joint from 2.3 MPa to 5.8 MPa, while the micro-micro-hierarchical joint specimen possessed a shear strength of as high as 14.5 MPa. Further, the adhesion of UP adhesive with the three-level hierarchical micromicro-nanostructured specimens increased so high that the joints started to deform plastically during the shear strength measurement, preventing the evaluation of their maximum strength. The silane-treated specimens displayed also significantly higher shear strengths and more cohesive failure than the corresponding untreated specimens. Silanization was also observed to improve the interaction of the UP adhesive with the aluminum nanostructure. The results demonstrate that the adhesion of polyester to aluminum surface can be significantly enhanced utilizing readily available and environmentally friendly methods.