Spectral and photophysical properties of thioxanthone (9H‐thioxanthen‐9‐one, TX) were determined in a few protic solvents (H₂O, D₂O, hexafluoro‐2‐propanol) and compared with those in aprotic solvents. On the basis of the time‐resolved and steady‐state emission measurements and available literature data, it has been shown that the dominant S₁‐TX deactivation process in protic solvents is the formation of the S₁‐complex. The important modes of deactivation of the S₁‐complex are fluorescence (ϕ_F≈0.4–0.5) and intersystem crossing to the T₁ state. The S₁‐complex→S₀ internal conversion plays, at most, an insignificant role in S₁‐complex deactivation, which is evidenced by the absence of an isotope effect of protic solvents on the lifetime and quantum yield of fluorescence.