We characterize the additive operators preserving rank-additivity on symmetry matrix spaces. Let $S_{n}(F)$ be the space of all $n; imes;n$ symmetry matrices over a field F with 2, $3;in;F^{*}$, then T is an additive injective operator preserving rank-additivity on $S_{n}(F)$ if and only if there exists an invertible matrix $U;in;M_n(F)$ and an injective field homomorphism $phi$ of F to itself such that $T(X);=;cUX{phi}U^{T},;forallX;=;(x_{ij);in;S_n(F)$ where $c;in;F^{*},;X^{phi};=;(phi(x_{ij}))$. As applications, we determine the additive operators preserving minus-order on $S_{n}(F)$ over the field F.