Gas phase protonation enthalpy (proton affinity) and deprotonation enthalpy of paracetamol, PA = 909.4 ± 8.4 kJ×mol-1 and ?acidH0 = 1430.3 ± 8.8 kJ×mol-1, have been experimentally determined by the extended kinetic method (EKM) using ESI-triple-quadrupole mass spectrometry. Gas phase basicity and acidity deduced from these experiments, GB = 869.9 ± 8.4 kJ×mol-1and GA = 1404.7 ± 8.8 kJ×mol-1 are in good agreement with calculations performed at the B3LYP level of theory with 6-311++G(3df,2p) and 6-311++G(d,p) basis sets. We also have derived the enthalpy of formation of deprotonated (?fH0(g) = -386.4 ± 9.0 kJ mol-1) and protonated (?fH0(g) = 346.3 ± 8.6 kJ mol-1) paracetamol ions. © ARKAT-USA, Inc.