The Brillouin scattering spectra in NaNO 2 have been studied using a Fabry-Perot interferometer. The observed Brillouin shifts for eighteen acoustic phonons in nine scattering geometries have been assigned to specific modes of vibration. The determined values of nine elastic constants in units of 10 10 dyn/cm 2 are C 11 =31.7, C 22 =58.2, C 33 =66.0, C 44 =12.4, C 55 =9.91, C 66 =4.79 ( C 66 D =4.98), C 12 =12.6, C 23 =17.4 and C 13 =19.7 at room temperature. The temperature dependence of C 22 D associated with the longitudinal phonon propagating along the ferroelectric b -axis has been studied with particular emphasis in the region close to the Curie and the Neel points. The elastic stiffness constant C 22 D showed anomalous decrease both at the Curie and the Neel temperatures. These results are compared with those obtained in the ultrasonic region.