The proteolytic activity of gut extracts prepared from Hyalomma excavatum female ticks was studied at different stages of blood feeding. Proteolytic enzyme activity was shown to be negligible in unfed ticks, increased from the onset of the tick feeding, reached a maximum at 60–70 hours post attachment and then declined to the initial low level. Proteolytic activity seems to be related to the presence of acidic protease(s) with an optimal pH of 2.9. It appears that a proteolytic enzyme inhibitor is present in the gut of the engorged tick which might be responsible for the low activity at the final stage of feeding.