We study an SO(5) model unifying p-wave superconductivity and ferromagnetis
m. If only a single p-wave pairing wave function is involved, the p-wave su
perconducting (pSC) and ferromagnetic (FM) states can be unified to form a
ten-dimensional multiplet of SO(5). The collective modes in pSC and FM stat
es are studied from this viewpoint in terms of a nonlinear sigma model. [S0
031-9007(99)08843-2].