Doctrine of music's Ethos is a phenomenon of musicalphilosophical thought of Antiquity, which combined such concepts as music and morality. Their interaction and mutual influence was examined by the Greek philosophy thoroughly and in detail. All known then music categories -- rhythms, music instruments and modes were divided on beneficial and harmful, depending on their influence on a psychological state of a person. Historical development of these ideas could be quite easily traced back to their first appearance in mythological form. Turning in the future from the religious and magical formulation to the philosophical ones, these ideas have acquired quite secular features. This evolution did not affect the basic ideas and even formal categories and attributes, which remained identical to their prototypes, set out in mythology. Despite this evidence of ancient Greek origin of the teaching of Ethos, versions of its foreign origin were put forward by some historians. The basis for this kind of speculations was the conviction of number of historians of foreign, mainly "Egyptian" origin of ancient Greek philosophy in general. Without going into detail on the issue of the source of ancient Greek philosophy, in this paper the question of the origin of the doctrine of music Ethos is considered. First of all -- the premises of the doctrine's emergence, caused by the existing problems in the life of Greek society and state, resulting in utilitarian character of the doctrine. The mythological sources, which had laid the theory's ideological foundation and which later would receive a philosophical form, are also discussed in detail. [ABSTRACT FROM AUTHOR]