After seeing his dog tumble into the well on Saturday, Say Phalla, the animal's 25-year-old owner, used a rope to descend in after it,The Cambodia Daily reported.
"He hurried to go into the well by using the well-rope to rescue his beloved dog, but he disappeared into the water," local police chief Pech Ngon Srin told The Daily.
His 64-year-old mother, who had been watching the rescue attempt, saw that her son did not re-emerge, went into the well after him and also drowned.
The family's 38-year-old neighbour then climbed down into the 9-metre deep well but slipped and fell, according to the report.
Several hours later authorities arrived to drain the well and foundthe bodies of the three Cambodians and the dog.