Small–angle neutron scattering (SANS) is a powerful technique to investigate critical phenomena, miscibility and phase transition of polymer blends because of the enhanced contrast between deuterium-labeled polymers and non–labeled polymers. Two SANS instruments, SANS–U (University of Tokyo) and SANS–J (JAERI) installed at the guide hall of the JAERI reactor JRR–3M, are available for the studies of polymer blends. Both instruments provide scattering data with a quality high enough to be used for detailed analyses of the polymer blends. Here we review two notable works of polymer blends performed with those two SANS instruments. Both works report new findings related to the singlephase states of polymer blends [1,2].