In this paper, we define the $4$-girth-thickness $θ(4,G)$ of a graph $G$ as the minimum number of planar subgraphs of girth at least $4$ whose union is $G$. We obtain the $4$-girth-thickness of the arbitrary complete graph $K_n$ getting that $θ(4,K_n)=\left\lceil \frac{n+2}{4}\right\rceil$ for $n\not=6,10$ and $θ(4,K_6)=3$.