Is there such thing as overdiversification of portfolio?

Yes, this is possible. I have answered this in a similar question previously. Here it is: https://seedly.sg/questions/hi-do-you-think-the...

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Yes, too much of everything is bad. The purpose of diversification is to lower the risk of losing signifcant portion of your portfolio during different economic periods. When over-diversify, you spread your investment too thinly into too many categories. Sure your risk will be lower, but your potential gains will be lower too.

An exaggerated example:

You think stocks are risky so you invests in T bills, T notes, Govt bonds, gold, silver, platinum, bitcoin, litecoin, ethereum, commercial REIT, hospitality REIT, residential REIT, option, futures...

Need to consider what you mean by over diversification - diversification of an investment portfolio aims to remove so-called nonsystemic volatility through holding many (hopefully uncorrelated) assets.

STI has 30 constituents (and is considered quite a narrow index), S&P500 has 500 (companies - holdings are slightly higher due to dual class shares) and some world stock ETFs have thousands of underlying holdings. A breadth of exposures is generally considered desirable for a long term investor.

However, if you are directly holding many different instruments (eg 30 different holdings, whether direct shares or managed funds or ETFs) then you start to lose track of entry time/price and less clear about overall strategy/asset allocation. That is obviously not desirable but that doesn't take away from underlying benefits of diversification.

Hi!

Yes, there is a chance that over-diversification takes place. Diversification refers to the process of investing in different asset classes to reduce the risk of the portfolio. This is because different asset classes (equity, debt etc.) show varying returns in the same situation. Thus, negatively correlated assets provide diversification benefits as the negative returns from one asset can be compensated by the positive returns in another category.
However, once the unsystematic or diversifiable risk has been eradicated, there is no benefit derived from adding more aseets into the portfolio. Now, the portfolio will be over-diversified.

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Hope you find this helful.