The Algerian gas condensate may be valuated as a raw matter to obtain maximum ethylene and propylene yields, the latter are used as first materials to produce polyethylene and polypropylene. It is judged utile to substitute ethane as pyrolysis feedstock by the Algerian condensate compounded with ethane. Several dilutions (5%, 10% and 20%) of the gas condensate and its fractions with ethane have been prepared to be used as pyrolysis feedstock. The effect of temperature, residence-time and steam flow on the yield of pyrolysis products have been studied well as their influence on the composition of pyro gas and liquid pyrolysis.