"In December, for the first time search revenue from mobile surpassed PC," Chief Executive Robin Li said in a statement.
Baidu forecast revenue of 12.65 billion-13.07 billion yuan ($2.04 billion-$2.12 billion) for the current quarter. Analysts on average expected revenue of 13.62 billion yuan.
The forecast reflects the combined impact of the late timing of Chinese New Year and increased contribution from mobile as a percentage of overall revenue, the company said.
Baidu is facing increased competition on smartphones as companies such as Alibaba Group and Tencent Holdings invest in apps and content to keep users engaged.
Others, including Qihoo 360 Technology and Sohu.com's Sogou, are moving aggressively into the search business.
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"The investments we've made in mobile over the last two years have clearly paid off and set the stage for Baidu to capture an even larger market opportunity," Chief Financial Officer Jennifer Li said in a statement.
Net income attributable to Baidu jumped 16 percent to 3.23 billion yuan, or $520.4 million, for the fourth quarter.
Excluding share-based compensation expenses, Baidu earned 9.97 yuan per share, or $1.61 per ADS, beating the average analyst estimate of 9.94 yuan per share, according Thomson Reuters I/B/E/S.
Baidu shares closed at $214.67 on the Nasdaq on Wednesday.