Patong Police were called to the scene at about 5:41pm.
Officers and rescue workers from the Kusoldharm Foundation arrived to find a blue Honda Click still on the road with signs of impact with the roadside concrete barrier.
The riders, Pathumkesorn Khunkaewsirisit, 28, and her sister, Pratumporn Khunkaewsirisit, 25, on the ground were far below after being flung over the barrier during the impact.
The two women were on their way to view a rental property below when the accident happened.
Ms Pathumkesorn, who was driving, reportedly struggled with the poor brakes on the motorbike and was unfamiliar with the steep slope, police said.
She lost control of the motorbike, causing both her and her sister to be ejected from the bike and over the edge of the road.
Emergency responders used ropes to abseil down to the two women and safely bring them back to the road.
Ms Pathumkesorn sustained a broken leg, while Ms Pratumporn suffered abrasions from the impact and subsequent fall.
Both were taken to Patong Hospital for further medical care.