In its physiological environment DNA is constantly exposed to mechanical stress. The nanomechanical properties of DNA influence not only its response to stress but also its interaction with proteins. Despite its crucial role in epigenetics, little is known about how methylation affects the nanomechanical properties of DNA. To investigate the impact of methylation on DNA nanomechanics, here we manipulated single molecules of chemically or enzymatically methylated DNA and compared their properties with those of non-methylated DNA. As a model we used a 3312-base-pair long sequence of lambda-phage DNA that met the criteria of a CpG island. Chemically methylated DNA was prepared with PCR containing 5-methyl-CTP in the reaction mixture. For enzymatic methylation the M.Sss.I methyltransferase was used. Single DNA molecules were mechanically manipulated with force-measuring optical tweezers in repeated stretch-relaxation cycles. Surface-adsorbed DNA molecules were studied by using atomic force microscopy (AFM). We found that the molecular contour length, bending rigidity and intrinsic stiffness were decreased in methylated DNA, pointing at structural and nanomechanical alterations. Furthermore, the cooperative overstretch transition was significantly longer in the methylated form of the molecule, suggesting that the dynamics of intramolecular rearrangements were also affected. AFM measurements of DNA molecules adsorbed to mica surface substantiated the significant reduction of molecular contour length in methylated DNA. By contrast, the apparent bending rigidity of the surface-adsorbed methylated DNA was increased, which is most likely caused by interactions between DNA and the mica surface. In sum, methylation leads to an axial compaction of the dsDNA structure, an increase in bending flexibility in the low-force regime and an increase in axial compliance at higher forces (>20pN). Conceivably, modulation of DNA structure and nanomechanics caused by methylation leads to a complex control of structural accessibility and association kinetics of DNA-binding proteins.