Historically the trust was a ``conveyancing`` device for real estates designed to avoid rigidities of intestacy and the tax burdens. But in late 19th century when financial markets started to produce new investment products, the trust underwent radical transformation. As the portfolio of financial assets displaced family land as a dominant form of trust property, the trust has become a ``management`` vehicle for holding such assets, and the nature of the trusteeship radically changed. The trustee was now required to perform ``active manager`` role rather than ``passive custodian`` role. The equity courts in UK and many states in US developed a series of trust investment law, reflecting the enhanced management discretion on the trusteeship. Korean Trust Act has also adopted similar stance as to investment law to Anglo-American style and equipped the Korean trustees with similar powers and duties. This article investigates among other things whether the standard of care on the Korean trusteeship should be that imposed upon a mandatee or that upon a voluntary bailee. It is argued here that the standard of care upon a trusteeship should be flexible enough to cover both bailee standard and mandatee standard. In investigating the standard issue, following issues are also researched: (i) the influence of the new financial products and the enhanced management powers on the trusteeship, and (ii) the separate development of trust investment law and fiduciary law that is triggered by the enhanced management powers. It is also argued here that although the Korean investment law is in a developing stage such as that of ``legal list``, it is possible for investors to impose ``prudent investor`` standard upon the Korean trustees by inserting such terms in a trust contract. On the other hand, it is argued in this article, that Korean fiduciary law is well developed to cover conflict of interest issues and expressly stipulated in the Korean Trust Act.