It was only the second time in Google's history it has missed Wall Street expectations.
Eric Schmidt, chief executive of Google, said the company had taken on more employees than it expected, adding 1,548 new staffers, many of them from the marketing industry.
Schmidt said: "We overspent against our own plan in the area of headcount. We hired a little faster than we planned."
"Was this a mistake or not? It was not a mistake, the kind of people we brought in are so good we're happy we did this. We'll watch it, adjust, be opportunistic, but we'll be careful about that."
Google also said lower than expected revenues from affiliates were partly to blame for a disappointing second-quarter.
The company's Adsense programme, where affiliate sites feature Google classified ads, reported growth of just 36% year-on-year.
In contrast, Google reported "particular strength" in revenues from its core Google.com products, with 74% growth year-on-year.
Gross revenues of $3.87bn (£1.9bn), up 58% year-on-year, were in line with Wall Street forecasts.
Schmidt said Google's international business, which it is seeking to boost, was "very very strong" -- 48% of its revenues now come from outside the US, up from 42% a year ago.
But, Google reported a 1% fall in revenues from the UK against the first quarter of the year. The UK now contributes 15% of total revenue earned.
However, it was not all good news in overseas markets, with Larry Page, the co founder and president of Google, conceding that the company had not been an "immediate success" in China.
Yet, Page predicted Google would reap victories in China and that it was already accelerating market share.