BlackRock Inc , the world's largest asset manager, reported a big jump in fourth-quarter profit and revenue on Tuesday, aided by the global stock market rally.

Earnings, excluding certain items, totaled $670 million, or $3.42 per share, up 77 percent from $379 million, or $2.39 per share, a year earlier. Revenue jumped 61 percent to $2.49 billion.

And with markets on an upswing, the $3.6 trillion behemoth created when Chief Executive Laurence Fink bought Barclays Plc's investment unit for $15 billion just over a year ago finally appears to be paying off for investors.

People can see that they've been able to execute and integrate all these platforms now, said Elizabeth Bramwell, manager of the Sentinel Growth Leaders fund, which owns BlackRock shares. They have the ability to offer a diversity of products and geographic diversity that's just unparalleled.

Anticipating improving results, the shares of New York-based BlackRock have gained 16 percent over the past three months, closing at $193.58 on the New York Stock Exchange on Monday. The biggest upsurge followed Fink's comments at a conference last month that fourth-quarter profits would be very strong.

Still, the stock price remains well below $226.74, its close on December 1, 2009, when the deal for Barclays Global Investors was completed. Contrasted with BlackRock's 15 percent loss since then, the Standard & Poor's 500 Index has gained 16 percent.

It has taken a while for investors to catch on to the merits of the deal. BlackRock's operating margin excluding some items has been lower than expected when the deal was in process in 2009. The margin hit 40.7 percent in the fourth quarter but for all of 2010 was 39.3 percent, less than the 40 percent or more investors expected.

Fink has said he is plowing money back into the firm and warned investors in October that margins were unlikely to reach the 40 percent level in 2011. One key spending project, to allow BlackRock's managers and customers to cross trades on a private network known as a dark pool, is expected to begin operations later this year.

The firm's indexed equities unit has also been hurt by the drop-off in securities lending since the financial crisis. And low interest rates curtailed income from the firm's short-term cash management accounts.

Some investors have also been concerned with the amount of merger-related withdrawals from the combined firm, which totaled $121 billion in 2010, according to BlackRock. Many stemmed from clients who previously had accounts with both firms before the merger and felt uncomfortable leaving the same amount with one firm.

Fink has taken to calling the withdrawals merger dis-synergies, the opposite of the usual corporate lingo extolling merger synergies.

Analysts who track BlackRock follow the firm's preferred measure of profitability, which excludes costs from merger integrations and closed-end fund launches. Costs from compensation programs related to Bank of America Corp's Merrill Lynch and PNC Financial Services Group Inc

, both still shareholders in the firm, are also excluded.

Using generally accepted accounting principles, BlackRock earned $657 million, or $3.35 per share, in the fourth quarter, up from $256 million, or $1.62 per share, a year earlier.

(Reporting by Aaron Pressman; editing by John Wallace)