Ruthenium-doped PbTiO₃ {(1-x)PbTiO₃+x RuO₂, x=0-0.018, (PRT)} twin crystals were grown by the flux cooling method. The pyroelectric properties of the poled PRT crystals with x=0.005-0.009 were measured. The addition of RuO₂ markedly affected the crystal size and improved the crystal imperfections of PbTiO₃. Based on observations by scanning electron microscopy and the back-reflection Laue method, black platelike crystals with x=0.009, in particular, exhibited excellent crystallinity. Based on the results of identification and chemical analysis and measurement of pyroelectric properties, the limit of substitutional solubility of Ru⁴⁺ ions for Ti in PbTiO₃ was estimated to be in the vicinity of 1.1mol%. The figures of merit F.M. for voltage responsivity of pyroelectric IR sensors were satisfactory for samples with x=0.005-0.009; in particular, the sample with x=0.009 showed the highest F.M. of around 5.5×10^-11C·cm/J, which was nearly equal to those of PMT (x=0.045) single crystals. Judging from the measurement of pyroelectric properties of the PRT crystals, crystals with x=0.009 are suitable as element materials for pointtype pyroelectric IR sensors.