Abstract　 　　
  Recent observations show the dramatic evolution of the sizes of massive quiescent galaxies : Massive quiescent galaxies at redshifts z~2 exhibit on average physical sizes smaller, by factors 3-5, than local ETGs endowed with the same stellar mass. There are two important questions involving the formation and evolution of massive ETGs arisen :1) How did the small size of massive ETGs form at high redshift? 2) How did the compact, massive ETGs evolve to ’catch up’ the local relation? I will show the main physical mechanisms for size evolution. And also I will also show the recent results up to redshift 4 based on HST WFC3 observations. The second part of this talk will introduce the morphology of X-ray selected AGN hosts at z~2. Compared with a control sample of normal galaxies with similar stellar mass and redshift, we find there is no morphological difference and no enhanced signal of major merger. We conclude that major merger may be not the main triggering mechanism for X-ray selected AGN at z~2.