Abstract Temperature-programmed desorption (TPD) of n-butylamine ( n-ba) has been used as a tool to investigate the nature of the active sites on the surface of a silica-alumina gel. On dry samples, at low temperature and short times of adsorption, the TPD spectra show two peaks: the first peak corresponds to n-ba weakly held that desorbs around 150°C whereas the second one is composed of propylene and 1-butene formed during the TPD at temperatures about 400°C. As temperature or time of adsorption is increased, a slow conversion of the first into the second peak is observed. At increasing adsorption temperatures, an intermediate peak develops around 300°C. When water is preadsorbed, the height and shape of the first peak change slightly, the change is more pronounced in the last peak and is very important in the intermediate one. Conclusions about the nature of the active sites on the surface are drawn from these experimental facts. Finally, apparent activation energies of desorption for the first two peaks are calculated.