According to the human-rights group's latest report on the death penalty worldwide, China carried out at least 1,770 executions.
However, Amnesty said the real figure was probably higher.
A Chinese legal expert was quoted as saying the true figure was closer to 8,000.
In its annual report, released on Thursday, Amnesty said that China, Iran, Saudi Arabia and the US remained the world's leading executioners. Together the four countries accounted for 94% of last year's 2,148 documented executions.
While China accounted for the bulk of cases, at least 94 people were executed in Iran, 86 in Saudi Arabia and 60 in the US, the report said
China carries out executions by shooting or lethal injection, Saudi Arabia by beheading, Iran by hanging or stoning, and the US by electrocution or lethal injection.
Amnesty said its figures were approximate because of the secrecy surrounding the death penalty.
Many countries, such as China, refuse to publish full official statistics on executions while Vietnam has even classified statistics and reporting on the death penalty as a "state secret".
Amnesty says more than 20,000
are on death row worldwide
The report also stated that at least 2,148 people were executed during 2005 in 22 countries.
The figures are lower than 2004's where 3,797 were executed, but still higher than 2003, where 1,146 were executed.
According to Amnesty more than 20,000 people on death row around the world were waiting to be killed by their own governments.
"Figures around the death penalty are truly disturbing: 20,000 people are counting down to the day when the state will take their life," said Irene Khan, Amnesty International's secretary-general.:
"The death penalty is the ultimate, irreversible denial of human rights, because it contravenes the essence of human values. It is often applied in a discriminatory manner, follows unfair trials or is applied for political reasons," Khan said.
Singled out as particular cause of concern was Iran, which Amnesty said was the only country it knew of to have executed juvenile offenders last year. The US outlawed juvenile executions in March 2005.
Iran executed at least eight people in 2005 for crimes committed when they were children, including two who were still under the age of 18 at the time of their execution, the report said.
"The death penalty is the ultimate, irreversible denial of human rights, because it contravenes the essence of human values"
Amnesty International Secretary-General
Overall however, Amnesty said that while the number of executions had increased, the worldwide trend towards abolition of the death penalty continues to grow.
The number of countries carrying out executions has halved in the last 20 years and has dropped for the fourth consecutive year.
With the addition of Mexico and Liberia, 86 countries have now abolished the death penalty for all crimes, compared with 16 countries in 1977, Amnesty said.