Kyoto District Court condemned Chisako Kakehi, 70, to the gallows for the murder of three men -- including a husband -- and the attempted murder of another, ending a high-profile case that has gripped the country.
Kakehi became notorious after using the poison cyanide to dispatch a number of elderly men she was involved with, drawing comparisons with the spider that kills its mate after copulation.
"The accused made the victims drink a cyanide compound with a murderous intention in all the four cases," Judge Ayako Nakagawa told the court, according to public broadcaster NHK.
Nakagawa rejected defence lawyers' arguments that Kakehi was not criminally liable because she was suffering from dementia.
Prosecutors said she killed the men after they made her the beneficiary of life assurance policies that ran into millions of dollars.
She reportedly amassed one billion yen ($8.8 million) in payouts over 10 years but subsequently lost most of the fortune through unsuccessful financial trading.
She had relationships with many men, mostly elderly or ill, meeting some through dating agencies, where she reportedly stipulated that prospective partners should be wealthy and childless.
Kakehi, who is also known as "The Poison Lady", is said to have stashed some of her cyanide in a plant pot she later threw out.
They also found paraphernalia for administering drugs and medical books at an apartment she kept south of Kyoto.
Kakehi initially refused to speak when her trial began in June but later stunned the court by admitting killing her fourth husband in 2013.
"I killed him... because he gave other women tens of millions of yen but did not give me even a penny," she told the court, according to Jiji Press.
The accused earlier told judges she was ready to be hanged.
"Even if I were executed tomorrow, I would die smiling," Kakehi told judges.
But her lawyers reportedly plan to appeal to a higher court, suggesting the high-profile trial could yet drag on.
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