Spin wave dispersion relations in Fe3-xMnxSi ordered alloys have been measured by neutron scattering for alloys with x = 0.04 and x = 0.18. The dispersion relations have been found to be quadratic in the magnon wavevector q̄ up to about half of the Brillouin zone along  direction. The measured values of the spin wave stiffness constant are 169±7 meV Å02 and 207±7 meV Å02 for samples with x = 0.18 and x = 0.04, respectively. The energy gap found from the rough data turned out to be almost totally due to the triple-axis spectrometer resolution properties. The nearest neighbour exchange integral for FeFe interaction, calculated from the above data, equals to 22.5±1.0 meV.