The technological optimism that technological progress can complete humanity lies behind the movement of transhumanism. As long as transhumanism is based on technological optimism, the voices that worry about the imperfection of scientific technology and the destruction of human nature by (incomplete) science and technology will not stop. In this regard, transhumanists advocate human moral improvement. This means a radical transformation of human nature. There seems to be no consensus between bioconservatives who raised the question of the destruction of human nature as a serious ethical problem and transhumanists who argue that human nature can be changed (improved) rather than left fixed and unchanging. We first clarify the issue of the biologists and trans-humanists(Chapter 2). Next, we examine the meaning of `moral` in the moral enhancement and the principle of double effect(Chapter 3). Finally, we will reflect on the possibility of moral enhancement which newly implies the ethics of transhumanism(Chapter 4).