Electronic Journal of Differential Equations, Vol. 2005(2005), No. 33, pp. 1-4. Title: Fiber preserving transformations and the equation $y'''=f(x,y,y',y'')$ Authors: Raouf Dridi (Lille1 Univ., France) Sylvain Neut (Lille1 Univ., France) Abstract: In this paper, we give simple explicit conditions for a third order ordinary differential equation to be equivalent to the equations $y'''=0$ and $y'''+y=0$ under fiber preserving transformations. Submitted February 3, 2005. Published March 22, 2005. Math Subject Classifications: 58A15, 58A17, 58A20. Key Words: Cartan's method; equivalence problem; fiber preserving transformations.