Gu Kailai, the wife of prominent Chinese politician Bo Xilai, did not contest charges of poisoning British businessman Neil Heywood last year.
A verdict will be delivered at a later date, a court official said.
China Correspondent Angus Walker's report on Gu Kailai's trial:
Prosecutors said Ms Gu and Zhang Xiaojun - who was described in court as her accomplice - poisoned Mr Heywood last November after a business dispute.
The argument led Ms Gu to believe the British businessman was a threat to her son, Bo Guagua.
Mr Zhang had driven Mr Heywood to Chongqing from Beijing and prepared a poison which he later put into a glass of water. Later that day, the businessman met Ms Gu at a hotel, became drunk and then asked for water.
A court official said:
Gu Kailai believed that Neil Heywood had threatened the personal safety of her son Bo and decided to kill him. She poured a poison into his mouth.
The scandal has ended the political career of Mr Xilai, who was once considered a strong contender for membership of the highly influential nine-member Politburo Standing Committee and possible future leader of the country.
He was sacked from his position as head of the Communist party in March after allegations surfaced linking Ms Gu to Mr Heywood's death, and he remains under investigation by the party over corruption claims.