  In \cite{tva}, Bertrand Toen and Michel Vaquie defined a scheme theory for a
closed monoidal category $(C,\otimes,1)$. In this article, we define a notion
of smoothness in this relative (and not necesarilly additive) context which
generalizes the notion of smoothness in the category of rings. This
generalisation consists practically in changing homological finiteness
conditions into homotopical ones using Dold-Kahn correspondance. To do this, we
provide the category $sC$ of simplicial objects in a monoidal category and all
the categories $sA-mod$, $sA-alg$ ($a\in sComm(C)$) with compatible model
structures using the work of Rezk in \cite{r}. We give then a general notions
of smoothness in $sComm(C)$. We prove that this notion is a generalisation of
the notion of smooth morphism in the category of rings and provide some
examples of smooth morphisms in $N-alg$, $Comm(Set)$ and Comm(C).
