In order to measure differential cross sections of the 10B(n,α)7Li reaction induced by MeV neutrons using the forward-backward coincidence method, a thin film 10B sample was designed and the 10B atom number was determined with a reference 10B film sample. Alpha counts of the 10B(nth,α)7Li reaction from the 10B thin film and the reference sample were measured using a gridded ionization chamber and thermal neutrons, which were moderated and thermalized by paraffin from fast neutrons produced in D(d,n)3He reaction on a 4.5 MV Van de Graaff. The neutron flux was normalized by measuring the fission yield of a small 238U fission chamber.