The series of compounds RTiO3, R = Gd, Tb, Dy, Ho, Er, and Tm, were obtained as single-phase materials via solid state reaction between Ti2O3 and R2O3 at ca. 1500°C in welded molybdenum crucibles under argon; YbTiO3 and LuTiO3 could not be obtained as single-phase materials using this procedure. Lattice constants for all compounds were determined from powder X-ray data and are compared with previous results. All of these materials order magnetically between 30 and 70 K. From the appearance of the χ−1m vs T curve the type of order can be identified as ferrimagnetic. High-temperature susceptibility data have been fit to a two-sublattice molecular field model and the intra- and intersublattice interaction constants have been extracted. It is found that the TiTi interaction is ferromagnetic and relatively constant from R = Gd to R = Lu. Low-temperature magnetization field data suggest the existence of complex magnetic structures, large magnetocrystalline anisotropy, or both. The magnetic properties of the RTiO3 series are compared to those of the chemically similar and better-known RMO3 phases where M = Al, V, Cr, Mn, and Fe. The observed differences are shown to follow from the sign of the M-M interaction, which is ferromagnetic for M = Ti and antiferromagnetic for M = V, Cr, Mn, and Fe, together with the implications of the crystal symmetry for the R-M interaction.