Millimeter and submillimeter wave ESR measurements of Nd2BaNiO5 have been carried out at 1.8 K using a single crystal that was obtained by the floating-zone method. The measured frequency region is from 50 GHz to 1.2 THz. The measured magnetic field is up to 30 T. Several AFMR modes due to the 16-sublattice magnetic structure below TN are clearly observed. Changes of AFMR modes at Bc1 = 9.6 T and Bc2 = 16.2 T are observed. AFMR modes with an antiferromagnetic gap of about 240 GHz and 1 THz are observed.