Guided propagation of polarized neutrons has been observed directly in
magnetic CoZr/Al/CoZr trilayer deposited on Gd3Ga5O12 garnet substrat
e by using neutron reflectometry technique. The resonance observed in
the transmission spectrum of neutrons corresponding to two low order g
uided modes is in good agreement with theoretical predictions. A detai
led theoretical description of the guided propagation in thin-film neu
tron waveguides is also presented.