Vapor pressures of xanthene [CAS Registry No. 92-83-1] and phenoxathiin [CAS Registry No. 262-20-4] were measured in the temperature range from (318 to 382) K [(0.5 to 127) Pa] and from (318 to 373) K [(0.5 to 36) Pa], respectively, using a static method, in both crystalline and liquid phases. The vapor pressures of the crystalline phases of both compounds were also measured in the pressure range (0.1 to 1) Pa using the Knudsen effusion method. From the experimental results, the standard molar Gibbs energies and enthalpies of sublimation/vaporization, at T = 298.15 K, and the triple-point coordinates for these two compounds were derived. The enthalpies and temperatures of fusion were also determined using differential scanning calorimetry. To the best of our knowledge, vapor pressure data reported here are the first for crystalline phenoxathiin and for liquid xanthene.