That depends on the size of your other investments. If the property is worth $100,000 and your total assets are $1,000,000 with the rest in stocks, that one property is a reasonable level of diversification. If you already have a house worth $500,000 then taking money out of stocks to buy the rental is a bad investment. The above are but two very simplified examples. You need to figure out what is correct for your situation though - there is no one size fits all.