Abstract: In the ethical debate of human enhancement, transhumanism, with the point of supporting on the research and development of Human Enhancement Technologies (HET), tries to justify the ethical feasibility with the presumption of ethical naturalism, which is the mainstream thought of normality nowadays. It suggests an ethical individualism for the improvement of the physical or psychological conditions of human body, an utilitarianism for the universal improvement on social scale as well as the morphological freedom and the posthuman-aimed evolution. Bioconservatism disapproves of transhumanism on human enhancement, which develops into two critical stands, strong and weak. The strong one, against the ethical naturalism of transhumanism, forwards critiques of metaethics and normative ethics, which fails to raise a substantial challenge on transhumanism. The critique of Natural fallacy loses by its formality and the critiques from J. Habermas and F. Fukuyama lose by their transcendental intuition and anachronistic ontology. The flaws of the strong one lead to its failure on the justification for the prohibition on the R&D of HET and imply for the weak one, keeping a naturalistic and empirical attitude on HET and whose critiques are referred at the end of this paper.