This project concerns the testing, comparison and evaluation of three consolidants applied on sub-fossilized hippopotamus bones that are going to be displayed in open area. Thirty six samples of sub-fossilized bones of hippopotami of small stature have been chosen. These samples come from the pale palaeontological excavation of the Geology Department,University of Athens that takes place in the tableland of Katharo, at the Lasithi region in Crete Island. After the macroscopic observation for the evaluation of the osteologic fitment surface condition, the structure and the formation of the bones were studied by the means of Scanning Electronic Microscope (S.E.M.) coupled with Energy Dispersive Analyzer (E.D.A.X.). Moreover, it was measured the pH of the surrounding soil of the excavation site. In order to choose the most appropriate consolidant for the bones to be exhibited in situ, three different consolidants of different chemical composition have been applied on the samples that followed a procedure of accelerated ageing. The aim of these experiments was to simulate the conditions of the area that the consolidated bones would be exposed. The samples were divided into five groups: a) Four samples remained untreated and they were not undergone accelerated ageing. (reference samples) b) Eight samples were consolidated with the solution of Ca(OH)2. c) Eight samples were consolidated with the solution of silicone resin Rhodorsil RC-70. d) Eight samples were consolidated with the solution of Primal AC532K. e) Eight samples that were not being consolidated were undergone accelerated ageing. The samples (b), (c), (d) and (e) were subjected into four accelerated ageing tests in relation with variation of temperature (gradually rising), frost, relative humidity (RH) and the soluble salts (NaCl, Na2SO4 ). The results of these measurements were the output from the sample’s macroscopic and microscopic observation, from the measurement of porosity and the study of the weight – time diagrams. The comparative results after the accelerated ageing revealed that the samples treated Primal AC532K presented the best behaviour in the tests of temperature variation, soluble salts and frost. Moreover, the cohesion of the samples after treatment was improved while their colour remained invariable. On the other hand the samples treated with Rhodorsil RC-70 presented the best results in the tests of humidity variations and soluble salts. However, none of the three consolidants presented the required properties in order that these bones could be remained in situ. Therefore, the best consolidant should be combined with other measures taken, such as sheltering the site, continuous monitoring of it and replacement of the original finds with replicas.