The 26-year-old Russian raised her arms in triumph as she crossed the line in 1hr 29min 42sec, 18sec ahead of her nearest rival, China's Liu Hong, with Anisya Kirdyapkina of Russia taking bronze (1:30.13)
Earlier Kaniskina and teammate and world record holder Vera Sokolova were quickly at the front of a large pack on the 2km circuit course starting and finishing at the Gukchae-bosang Memorial Park in the South Korean city.
At the halfway point the pack had thinned considerably but there were still 13 athletes separated by just 1sec with Kaniskina in the lead in a time of 46min 16sec.
But soon after the 14km mark Kaniskina, world champion in 2007 and 2009, broke away and she had opened up a five-second gap over fellow Russian Anisya Kirdyapkina with a quarter of the race to go.
Her victory never looked in doubt as she found the strength to forge a decisive lead over the last 5km.
Sokolova finished well down the field in 11th place in a time of 1:32.13.
The 20km walk was the only medal event on day five of the world championships, which is not featuring any track and field action.
Kaniskina's win lifts Russia to four golds in the championships, the same as medal table-toppers the United States.
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