Dynamic mode atomic force microscopy with frequency-shift detection has been employed for imaging single-stranded DNA on mica surfaces under ultrahigh vacuum conditions. For the wet procedures used to prepare the samples, the strong adhesion force caused by the water layer at the surface is observed even in ultrahigh vacuum conditions. The DNA images can only be obtained with large frequency shifts, but provide sufficient resolution to see the coil or higher-order structures of the DNA molecules in detail. Contrast effects, which might include information on the detailed structure, are often observed depending upon the feedback conditions.