Xi is expected to become China's next leader during party meetings next month, China's state-run Xinhua News agency reported.
He appeared Saturday at activities at Beijing's China Agricultural University celebrating National Science Popularization Day, where he called for the public to increase its knowledge about food and health.
He encouraged agrotechnology workers to continue working to increase the country's innovation and international competitive power.
"With a huge population and scarce land and water resources, our country must rely on technology to ensure the supply of agricultural products," Xi said.
On Thursday, Xi was cited in state-run media for the first time in 12 days, the BBC reported.
During his public absence, Xi canceled a meeting with U.S. Secretary of State Hillary Clinton and three other foreign dignitaries. Web searches for his name had been blocked.
The reason for his disappearance was not clear.
A number of sources told The Daily Telegraph that Xi, 59, had suffered a mild heart attack but was "recovering well." Other sources suggested that he had been busy consolidating his position in the weeks before he takes over as president from Hu Jintao.