GHANEM, Rabab2024-10-012024-10-012024-06http//localhost:8080/jspui/handle/123456789/12012The objective of this work is to study the existence of bifurcations of zero-Hopf type at the so-called Chen–Wang differential system y x y            z z  , , y  x 2  xz  3 y 2  a . The main tool up to now for studying a zero-Hopf bifurcation is to pass the system to the normal form of a zero-Hopf bifurcation. Our analysis of the zero-Hopf bifurcation is different; we study them directly using the averaging theory. In the second part of this work, we study the existence of zero-Hopf bifurcations of a Lorenz-Haken system in 4 R the averaging theory.enZero-Hopf bifurcation, Periodic orbit, Differential system, Averaging theory.Thesis