Poly(dG)-poly(dC) DNA and G4-DNA are two types of synthetic molecules that are regarded as promising candidates for molecular nanodevices. In this work, vibrating scanning polarization force microscopy (VSPFM) was employed to study the radial deformability of these two molecules coadsorbed on a Ni2+-modified mica surface. The values of the radial compressive elastic modulus of these two types of molecules were found to be similar (similar to 5-10 MPa) when the external loading force was between similar to 0.04 and similar to 0.12 nN. However, G4-DNA molecules possessed higher stiffness than poly(dG)-poly(dC) DNA (similar to 20-40 vs similar to 10-20 MPa) when the loading force was larger than similar to 0.12 nN. The results will aid us in understanding these molecule's mechanical performances.