We study the properties of a large sample of edge-on galaxies with high radial-to-vertical scale ratio in their stellar disks, which we call superthin galaxies. Several dozens of such galaxies were selected from EGIS catalog (edge-on galaxies selected from the Sloan Digital Sky Survey). Here we present spectral observations (R ~ 5000) of more than 20 superthin galaxies performed with the DIS spectrograph at the Apache Point Observatory 3.5m telescope. The superthin galaxies are found to be similar to low surface brightness disk galaxies. We use the structural parameters of edge-on stellar disks to constrain modeling of ionized gas rotation curves of the galaxies. We discuss some properties of the dark halos in superthin galaxies that canbe responsible for the formation and evolution of this rare type of objects.