Neutronics experiments on annular blanket systems that use a pseudoline source are performed. The shape of the annular blanket system is a rectangular parallelepiped (1300 × 1300 mm2 and 2040 mm long) with an inner cavity of 425.5 × 425.5 mm2 and 2040 mm long. The annular blanket consists of a 15-mm-thick first wall (Type 304 stainless steel) and 406-mm-thick breeder zone (inner lithium oxide and outer lithium carbonate). Deuterium-tritium neutron sources are set at the center of the inner cavity of the annular blanket system, and the pseudoline source is obtained by oscillating the annular blanket system back and forth in a 2-m span. Three annular blanket configurations are examined: the reference blanket, a blanket covered with 25-mm-thick graphite armor, and an armor blanket with a large opening (376 × 425.5 mm). The neutronics parameters of tritium production rate, neutron spectrum, and activation reaction rate are measured with specially developed techniques, including a multidetector data acquisition system, a spectrum weighting function method, and a ramp-controlled high-voltage system. Measured parameters are compared among three different configurations of the experimental system and also with the results of a closed geometry with a point source. A calculation with the GMVP Monte Carlo code that uses the JENDL-3 nuclear data library is performed and shows agreement within 10%. The current experiment provides unique data for a higher step of benchmark to test the ability of neutronics design calculations for a realistic tokamak reactor.