机构投资者指的区别于个人投资者，凡是公司性质的投资者都可称为“机构投资者”，包括境内外。

Institutional investors are entities that have large amounts of funds to invest for an
organization, or on behalf of others. This is in contrast with private investors.

广义的讲，机构投资者指为广大受益人或投资者的利益进行高成交量和低手续费的大宗交易的公司或者机构，包括投资中介机构（共同基金、投资银行和私募基金等）、契约性储蓄机构（社会保障基金、保险基金等）、存款机构（商业银行等）以及各种基金组织和慈善机构等等。在狭义上看，机构投资者就是许多西方国家管理长期储蓄的专业化的金融机构。这些机构尤其管理着养老基金、人寿保险基金和投资或单位信托基金，其资金的筹集和运用都是由专业人士完成。

"Institutional investors are organizations which pool large sums of money and invest those sums in companies. They include banks, insurance companies, retirement or pension funds, hedge funds and mutual funds. Their role in the economy is to act as highly specialized investors on behalf of others. For instance, an ordinary person will have a pension from his employer. The employer gives that person's pension contributions to a fund. The fund will buy shares in a company, or some other financial product. Funds are useful because they will hold a broad portfolio of investments in many companies. This spreads risk, so if one company fails, it will be only a small part of the whole fund's investment. Institutional investors will have a lot of influence in the management of corporations because they will be entitled to exercise the voting rights in a company. They can engage in active role in corporate governance. Furthermore, because institutional investors have the freedom to buy and sell shares, they can play a large part in which companies stay solvent, and which go under. Influencing the conduct of listed companies, and providing them with capital are all part of the job of investment management."

From http://en.wikipedia.org/wiki/Institutional_investor

机构投资者指保险基金、养老基金和证券投资基金等以机构身份从事证券投资的投资者。机构投资者通常具有集中性、专业性的特点，比较注重理性投资和长期投资，因而是稳定股市的重要力量。YJB
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机构投资者是与个人投资者相对的一个概念，即按投资者的性质进行分类，当证券持有人是自然人时，称该投资者为个人投资者，当证券持有人是机构时，称该投资者为机构投资者。目前，国内市场的机构投资者主要包括:证券公司、保险公司、证券投资基金、社会保险基金、合格的境外机构投资者（QFII），以及其他一般法人机构。机构投资者投资行为较为规范，具有较强的资金实力，可以进行组合投资，分散风险，并实行专业化管理。YJB