A court official told reporters Gu Kailai had not contested the charge that she killed Neil Heywood by poisoning in 2011.
The date of the verdict would be announced later, the official said.
Gu Kailai is the wife of former high-flying politician Bo Xilai, whose career in office was ended by the scandal surrounding Neil Heywood’s death.
Gu Kailai, herself a prominent lawyer, is on trial along with her aide, Zhang Xiaojun, who was described by the court as an accomplice.
Two British diplomats were in court to observe the trial, but no foreign media were given permission to attend.
In an unusual news briefing outside the court, the court official, Tang Yigan, said Gu Kailai and Zhang Xiaojun “did not raise objections to the facts and the charges of intentional homicide”.
Reading from a statement, Tang Yigan said the prosecution alleged that Gu Kailai had been involved in a business dispute with Neil Heywood, and believed he had “threatened the personal safety of her son… and decided to kill him”.
The prosecution alleged she had arranged for Neil Heywood to travel to Chongqing from Beijing, accompanied by Zhang Xiaojun.
Gu Kailai spent the evening of 13 November with Neil Heywood at the Nanshan Lijing Holiday Hotel, where they drank tea and alcoholic drinks.
“After Heywood became intoxicated, vomited and asked for a drink of water, she poured a poison into his mouth that had been prepared beforehand and that she had given to Zhang Xiaojun to bring along, causing Heywood’s death,” said the statement.
“The facts of the crime are clear and backed by ample evidence,” it said.
Tang Yigan said Gu Kailai had been “in good shape and mentally stable,” throughout the trial.
“The trial committee will announce the verdict after discussion,” he said.
The two defendants face a possible death penalty if found guilty.
China’s state news agency Xinhua later reported that four police officers would go on trial on Friday, accused of trying to protect Gu Kailai from prosecution.
Neil Heywood’s body was found at the hotel in Chongqing in November 2011.
The death was recorded as a heart attack at the time, but four months later Bo Xilai’s right-hand man, police chief Wang Lijun, fled to a US consulate to allege murder and a massive cover-up.
Bo Xilai was the Communist party head in Chongqing at the time of Neil Heywood’s death.
He had been seen as a strong contender for one of China’s top jobs, as the country prepares to install a new generation of leaders.
But he was sacked in March and is currently under investigation for unspecified “disciplinary violations.
The facts of the case may be as they have been reported by the court, but that there is a strong political element to the story.
The case raises questions about corruption at the highest level, so it is almost certain that this will be a politically managed trial as well as a criminal one.
The court may take into account mitigating circumstances in its verdict, he adds, including the assertion that Gu Kailai had been concerned for her safety and that of her son.
Gu Kailai, Zhang Xiaojun and Bo Xilai have not been seen in public since April, when the investigation was announced.
One of Gu Kailai’s supporters, who gave his name as Mr. Han, criticized the process of the trial, and said she should have been allowed to choose her own lawyer rather than accept one appointed by the court.
“She should have been granted the right to defend herself to the media,” he said.
“I won’t accept any verdict before I hear their side of the story.”
But there was a mixed reaction on Chinese social media, with many posts expressing satisfaction at the verdict.
“All the corrupt officials try their best to sing the praises of the present system, but I wonder what they say now after they have been tried!” said Lian Zhugen on Weibo, the Chinese version of Twitter.
The trial is being held in Hefei, 1,000 km (650 miles) from Chongqing.
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