“The concept of Logos at Heraclitus. The analyze of B1 fragment”. “Logos” is the most important word in the Heraclitus’ philosophy. One can tell, that Heraclitus is the philosopher of logos. The way of interpretation of this notion influences the comprehention of all work of the Greek thinker. The word appears eleven times in the following fragments : B 1, B 2, B 31, B 39, B 45, B 50, B 72, B 87, B 108, B 115 [numeration of Diels-Kranz]. Logos contains several notions, and it can not be reduced to one, as for exemple reason, speach, fire or god. The analyse of B1, where the logos apperas for the first time, shows the complexity of this term.