Behavior of low molecular mass poly(ethylene glycol) (PEG) polymer, i.e. molar masses Mn = 400 and 1000, in heavy water is studied by small-angle neutron scattering (SANS). Some part of the polymer molecules in concentrated solutions is found to form aggregates with size exceeding 30 nm. The form-factor of Gaussian coil is used to describe low concentrated PEG solutions. Virial coefficients are obtained from approximation of experimental SANS data for PEG solutions with concentration higher than 3% where the interparticle interaction effect is well observed.