The three men were accused of trafficking drugs from northern China
Three Japanese citizens have been executed in China for trying to smuggle the drug methamphetamine.
This follows the execution of another Japanese drug smuggler on Tuesday.
Following the latest executions, Japan's Justice Minister Keiko Chiba said she was concerned about the effect on relations between the two countries.
China is thought to execute more people than any other country in the world, although the government does not release overall figures.
The three latest Japanese nationals to be executed were smuggling the recreational drug from the north-eastern province of Liaoning, according to China's Xinhua news agency.
One of them, Teruo Takeda, bought 5kg of the recreational drug in 2003.
The 67-year-old then arranged for the other two - Hironori Ukai, 48, and Katsuo Mori, 67 - to take the consignment to Japan.
But they were caught at two separate airports in Liaoning.
On Tuesday, China executed Mitsunobu Akano, the first Japanese citizen to be executed since the two countries re-established diplomatic ties in 1972.
Ms Chiba, Japan's justice minister, said she was "concerned about relations between Japan and China when I think of the uncomfortable feeling or reaction felt by a majority of the Japanese people".
But the Tokyo government as a whole seems to have played down the issue.
Japan also has the death penalty, but not for drug smuggling.
Last week, the human rights organisation Amnesty International challenged the Chinese government to say exactly how many people it kills.
Claudio Cordone, of Amnesty International, said: "The Chinese authorities claim that fewer executions are taking place.
"If this is true, why won't they tell the world how many people the state put to death?"
China's Supreme People's Court has to approve all death sentences in a rule introduced in 2007 to avoid miscarriages of justice.