Recent experimental results for steady state operation research in JT-60U are presented with emphasis on extension of sustained duration of high performance. The duration of heating has been extended from 10 to 30 s, and plasma properties and dynamics have been investigated in a long time scale exceeding the current diffusion time and close to the wall saturation time on ELMy H-mode, high βp H-mode and reversed shear H-mode regimes. The duration of sustainment of high beta and/or a large fraction of bootstrap current has been extended. The particle control with the saturated wall has been studied. Development of real-time control of q profile and effects of toroidal rotation on ELMs and the QH-mode are also discussed.