The 61-year-old died after the collision yesterday in the popular Amphawa district of coastal Samut Songkram province, around 80 kilometres southwest of Bangkok.
The group were on a tour to see fireflies on the Mae Klong river, in an area also popular for its floating market and homestays, when their boat crashed into an empty vessel, district police officer Wattana Nualsrida told AFP.
"She was pronounced dead at hospital after suffering from brain injuries," the officer said.
The other two injured passengers were Hungarians, Wattana said.
The Hungarian embassy in Bangkok confirmed that one of its citizens was killed in a boat accident but could provide no further details.