AbstractElectron cyclotron emission (ECE) diagnostic systems in JT-60U for the measurement of electron temperature perturbations and the results of the measurement are described. In 1999, the heterodyne radiometer system was upgraded, and the number of the channels was doubled to 24. It can now measure ECE ranging from 176 to 200 GHz. The heterodyne system enables the measurement of the location and structure of the magnetic island, which is observed in the steady state high βp H-mode discharges. Behavior of an m/n=1/1 mode and sawtooth oscillations during electron cyclotron heating and electron cyclotron current drive is investigated by using the grating polychromator. Here, m and n are poloidal and toroidal mode numbers, respectively. It is found that magnetic island width with m/n=1/1 is decreased during electron cyclotron (EC) wave injection. It is also found that sawtooth period is significantly expanded by EC wave injection near the q=1 surface. The obtained maximum sawtooth-free period was about four times longer than the theoretically predicted one.