We report on a useful technique for reproducibly straightening and fixing DNA molecules. When a droplet of DNA solution on surfaces is sucked up by pipet, surface tension at the moving air-water interface is sufficient to stretch the molecules. The point of this technique is the interaction control between surfaces and DNA molecules by polymer coating. With polymers containing pi-conjugation units (polyphenazasiline, PPhenaz and poly(vinylcarbazole), PVCz), many DNA were nicely stretched and fixed on surfaces. Furthermore, structural changes of pi-units in polymers affected DNA-stretching and fixation. By using atomic force microscopy (AFM) and scanning near-field optical/atomic force microscopy (SNOM/AFM), the feasibility of this technique for DNA observations was demonstrated.