The study reveals the ideas of the remarkable Romanian scientist from Bessarabia, Bogdan Petriceicu Hasdeu (1838-1907), regarding the scientific research methodology of history and the model of the professional historian. It is exposed Hasdeu's methodological triad theory and the principles of the scientific method of research in history, chosen by the distinguished encyclopedist, based on the historiographical conceptions of his predecessors Giovani Batista Vico, Leopold von Ranke, Gheorg Hegel, etc. An increased attention is offered to his own visions regarding his professional qualities which a historian should posses as a specialist, considered by the outstanding B.P. Hasdeu, “laborious and artist in the same time”. The study presents some illustrative examples of practical manifestation of objectivity, correctness and scientific principledness, selected from the personal experience of historian and eminent researcher of Bogdan Petriceicu Hasdeu.