During the eighteenth century 'the nature of man' was the critical subject to the philosophes. Julien Offray de La Mettrie(1709-51), French physician-philosophe, argued his mind-body theory on the basis of his medical experiences and scientific knowledge. He developed his materialistic view to explain man's soul. His infamous work L'Homme Machine in which he dealt with his mind-body theory is the source for understanding of La Mettrie's philosophy. In this paper I study the relationship between the mind-body theory of La Mettrie in his L'Homme Machine and the eighteenth century biology. First, as a background of his theory, I discuss the significance of his career as a physician. Then, his characteristic argument is considered: soul is body-dependent, man is an animal, and mind is a property of organized matter of man. Also, I consider some of his biological experiments and theories, and point out their meanings in his thought. In conclusion, I suggest that even though La Mettrie was the first man that materialized soul and explained life and mind as properties of organized matter overcoming the dilemma of mechanical philosophy, and though his theory was influenced by the 'sciences de la vie,' it was not the only solution of mind-body problem in the eighteenth century milieu.