The effects of interface roughness for several multilayers are evaluated from measurements of neutron reflectivity and transmissivity as a function of momentum transfer, together with the profiles of the reflected and transmitted neutron beams. The multilayers are fabricated by vacuum evaporation onto polished Si substrates, whose roughness is measured with another optical technique. The multilayer samples are: (1) Ni/Ti with a period of 100 Å, and 100 layers evaporated on a rough Si substrate, (2) a Ge/Ti multilayer with 36 layers and a 200 Å period evaporated on sample 1, (3) a Ni/Ti multilayer with 52 layers and a 100 Å period on a smooth Si substrate, and (4) a V/Ti multilayer with 8 layers and a 400 Å period on a smooth Si substrate. The neutron measurements are carried out using a reflectometer at JRR-3M at JAERI. The reflectometer is a θ — 2θ scanning-type using a 12.6 Å neutron beam. The comparison between the experimental neutron reflectivity with that calculated using a one-dimensional optical method with a modified optical potential is also discussed.