The 300 losses represent about a fifth of the DoubleClick workforce, and are solely in the US.
However, Google warned that there may be more cuts as the search giant reviews DoubleClick's operations outside the US.
"Since our acquisition of DoubleClick closed on 11 March we have been working to match and align DoubleClick employees in the US with our organisational plan for the business," said Google in a statement.
"As with many mergers, this review has resulted in a reduction in headcount at the acquired company."
Google chief executive Eric Schmidt had warned about the probability of job cuts last month as part of the merger process.
The company has also said that it wants to sell off a DoubleClick operation called Performics Search Marketing as this conflicts with Google's existing business.
iTnews Executive Retreat - Security Leaders Edition
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