The 34-year-old woman was found early Monday morning on a road near a rubber plantation in eastern Thailand.
Her body was found next to her motorcycle and injured baby, police said.
“She was killed instantly at the site, her son sustained a broken leg and is now in hospital,” Police Lieutenant Pramote Kongnantha.
The officer said the elephant is believed to have retreated back into a nearby national park after the incident.
Rubber tappers work early in the morning often on land that edges onto forest, home to elephants and other wild animals.
A park official at Khao Soi Dao, one of several protected areas in the province bordering Cambodia, said it was unclear whether the elephant was the same animal that killed two Thai men on a rubber plantation in the province last October.
Conservationists estimate Thailand is home to around 2,500 wild elephants.But the population has been decimated over the past century in the face of rapid development, habitat destruction and the lust for ivory used to make medicine and ornaments.
Both wild and domesticated elephants, of which there roughly 4,000, have been known attack passersby and overturn cars, especially during mating season.
Last August an elephant in northern Thailand killed his Thai keeper, or “mahout”, before taking off into the jungle with three Chinese tourists still on his back. The tourists survived in the incident.