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The world number 12 American was first seed for the event and lived up to the billing as she dominated a plucky Doi 6-4 6-2.
Second seed Doi cruised to the final dropping just 14 games on the way, but she would win just six in the match against Williams.
The seven-time grand slam winner looked dominant from the start as Doi struggled to come to terms with her serve.
The American won 67 per cent of points on her first serve and saved six out of nine break points when Doi was able to get into Williams' serve.
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Doi showed resilience of her own saving six break points, but that was not enough for her to avoid being broken six times throughout the match as Williams powered home in the second set.
Williams took an early break in the second set after comfortably keeping her distance from the Japanese in the first.
But Doi fought back to 2-2 before Williams stepped up a gear and left the Japanese star in her wake.
The 35-year-old cruised through the next four games to seal the win and her 49th career title.
Williams said she was honoured to headline the return of women's tennis to Taiwan, and hinted her sister, world number one Serena, might make the trip next time.
"It's wonderful to have women's tennis here. It's been too long, it's the first time in 22 years," the number one seed said.
"It's my first time in Taiwan, so thank you for making me feel so welcome and thank you for making me feel at home.
"I might invite my sister to come here and play next time."