Reports in Japan say as many as ten men that she was either in a relationship with, or associated with, are known to have died.
Ms Kakehi had previously expressed her sorrow - and innocence - when her lovers died of what was believed to have been natural causes between 2007 and 2013. However, at the same time, she also accepted an estimated Y1 billion (£6,8 million) in insurance payouts and inheritances.
At the start of the trial, Ms Kakehi's lawyers said she could not be held responsible for the crimes as she suffered from dementia. The prosecution acknowledged she had mild dementia, but they insisted Ms Kakehi was fit to stand trial.
She admitted that her motive for killing Mr Kakehi was to inherit his money so that she could pay off her debts, adding that she was treated poorly during her marriage with regards to money. Ms Kakehi told the court that she may have put the poison in a health food capsule which she tricked her husband into taking.
The trial is expected to last until November.