The isotropic 3-space which is one of the Cayley-Klein spaces is obtained from the Euclidean space by substituting the usual Euclidean distance with the isotropic distance. In the present paper, we give several classifications on the surfaces in with constant relative curvature (analogue of the Gaussian curvature) and constant isotropic mean curvature. In particular, we classify the helicoidal surfaces in with constant curvature and analyze some special curves on these.