The ionization constants (proton gain) of 3-,4-, and 5-amino-1-(substituted phenyl)pyrazoles, have been measured in 10% v/v ethanol-water. pKa values show a good linear dependence on Hammett substituent constants. The reaction constants Q are in keeping with the respective protonation sites in the three series of monocations. The uv spectra of 1-(m-nitrophenyl)pyrazole and 1-(p-methoxyphenyl)pyrazole and of their 3-amino, 4-amino, 5-amino analogues recorded in acidic and neutral media, show that in the three series the first protonation site does not change with change in substituent at phenyl ring.