  We work out domain walls in neutron $^{3}P_{2}$ superfluids realized in the
core of neutron stars. Adopting the Ginzburg-Landau (GL) theory as a bosonic
low-energy effective theory, we consider configurations of domain walls
interpolating ground states, i.e., the uniaxial nematic (UN), D$_{2}$-biaxial
nematic (D$_{2}$-BN), and D$_{4}$-biaxial nematic (D$_{4}$-BN) phases in the
presence of zero, small and large magnetic fields, respectively. We solve the
Euler-Lagrange equation from the GL free energy density, and calculate surface
energy densities of the domain walls. We find that one extra Nambu-Goldstone
mode is localized in the vicinity of a domain wall in the UN phase while a U(1)
symmetry restores in the vicinity of one type of domain wall in the D$_{2}$-BN
phase and all domain walls in the D$_{4}$-BN phase. Considering a pile of
domain walls in the neutron stars, we find that the most stable configurations
are domain walls perpendicular to the magnetic fields piled up in the direction
along the magnetic fields in the D$_{2}$-BN and D$_{4}$-BN phases. We estimate
the energy released from the deconstruction of the domain walls in the edge of
a neutron star, and show that it can reach an astrophysical scale such as
glitches in neutron stars.
