||Efficient market hypothesis belongs among controversial economic concepts. Existence of regularly repeated financial crisises is a certain challenge to this concept. Some economists consider the existence of financial crisises as a proof of market inefficiency. Another explanation is contrary, that financial crisises balance previous market deviation back to equilibrium. We introduce a problem of market efficiency by presenting its theoretical concept. The major goal of the presented work is set on evaluation of change in market efficiency assumptions fullfillment during a financial crisis in conditions of a financial market of the Czech Republic.