Null designs on the poset of dual polar spaces are considered. A poset of dual polar spaces is the set of isotropic subspaces of a finite vector space equipped with a nondegenerate bilinear form, ordered by inclusion. We show that the minimum number of isotropic subspaces to construct a nonzero null t-design is ${prod}^{t}_{i=0}(1+q^{i})$ for the types $B_N,;D_N$, whereas for the case of type $C_N$, more isotropic subspaces are needed.