Magnetization and neutron scattering measurements have been carried out on an antiferromagnet Ba2CoSi2O7. The observed magnetic excitation is almost dispersionless, and the neutron intensity is only modulated along the  direction. The dispersionless magnetic excitation suggest that the Ba2CoSi2O7 system is a quasi-one-dimensional antiferromagnet. Classical spin-wave theory for a one-dimensional antiferromagnet can explain the dispersionless spin excitation. The magnetic structure determined by the measurement of the neutron powder diffraction is consistent with no observation of the multiferroic property in this system.