Ben Glisan, formerly treasurer at energy trader Enron, has become the first executive to be jailed for his part in the huge financial scandal at the firm.
Enron's former top management remain at liberty
Mr Glisan was sentenced to five years in prison after pleading guilty to criminal conspiracy.
"I think I would simply like to say I take full responsibility for my actions," Mr Glisan told the judge.
His conviction, prosecutors hope, could accelerate the cases against other more senior Enron ex-officials, notably former chief financial officer Andrew Fastow, his boss at the firm.
Mr Fastow is named in the same indictment as Mr Glisan, and is accused of having been the mastermind of the extraordinarily complex financial trickery that brought about Enron's collapse almost two years ago.
Hoping for a catch
There is concern in the US that the case against Enron's former management is proceeding slowly.
Michael Kopper, another former middle-ranking financier, has also pleaded guilty to conspiracy, but is not due to be sentenced until February next year.
Meanwhile, former chairman Kenneth Lay and former chief executive Jeffrey Skilling are under investigation, but have not been charged with any offence.
Prosecutors hope that, by successfully proceeding against smaller officials, they will eventually be able to build up a cast-iron case against the top management.
But Mr Glisan has not cut a deal to cooperate with investigators, meaning that his conviction may not advance the overall inquiry as far as some had hoped.
Several inquiries into Enron's fall from grace are under way.
The most promising, from the prosecutors' point of view, focus on the network of off-balance-sheet partnerships that were used both to siphon money from the firm and to inflate its apparent earnings.
Mr Glisan was charged with two dozen counts of money laundering, fraud and conspiracy for taking part in one of the secret partnerships.
In addition to his sentence, he is handing back almost $1m in illegal profits from one of the partnerships.