We introduce Chen inequalities for slant Riemannian submersions from cosymplectic manifolds onto Riemannian manifolds. We provide trivial and non-trivial examples for slant Riemannian submersions, investigate some curvature relations between the total space, the base space and fibres. Moreover, we obtain Chen-Ricci inequalities on the vertical and the horizontal distributions for slant Riemannian submersions from cosymplectic space forms.