The small-angle neutron scattering is used to measure the spin-wave stiness in the eld-polarized state of Dzyaloshinskii-Moriya helimagnet Cu2OSeO3, which is ordered below TC = 58 K. The Dzyaloshinskii-Moriya interaction reflects itself in the anisotropic form of the spin wave dispersion:
q = A(q - ks)2 +gB(H -HC2) that is seen as two round spots of the scattering intensity, though overlapping, on the left and right sides of the incident neutron beam. The spin wave stiffness is equal to 76 +- 1 meV A^2 at low temperatures and decreases slowly with temperature showing softening up to 39 +- 3 meV A^2 close to TC. The temperature behaviour of A resembles that of the
both archetypical helimagnet MnSi and archetypical ferrimagnet Fe3O4, supporting the concept of the strong spin interactions within Cu4 - tetrahedra, representing an essential magnetic building blocks of Cu2OSeO3 and thus forming its magnetic energy landscape.