The content of this paper includes an analysis of basic principles and validity of the Marxist sociological theory. In the Introduction, there is explained a problem of acquiring knowledge as well as the possibilities of establishing theories in social sciences, with a special attention paid to the possibility of gaining unconditional truth and question about an influence that personal values can perform in the work of a scientist. In the second part of the paper, there are given the basic principles of the Marxist social theory, there are explained the ideas of class-struggle, bourgeoisie economy and capitalistic type of property with the origin and type of functioning of the proletariat and historical necessity of establishing a classless society. The third part of the paper establishes a critique of Marxist sociology from the standpoint of its scientific validity. A special attention is paid to the way of functioning its basic principles and the problem of establishing the unquestionable facts in social sciences. In the conclusion, it is explained the substantial difference between science and ideology, and, it is indicated the necessity of establishing unconditional criteria for the recognition of scientific facts.