Emma McDade and Mariska Silkowski (both 10) cycled from Rothesay to Ettrick Bay and back in the pouring rain, in a time of two hours and 34 minutes.
Emma and Mariska took on this challenge during their recent Easter school holidays, as part of Autism Awareness Month.
Autism is important to Emma because her brother Lewis McDade (6) was diagnosed with the condition a year and a half ago.
Emma’s proud mum Claire Dickson is delighted that her daughter decided to do the fundraiser with her friend.
She said: “I’m proud. For her to come up with something like that on her own is a great achievement.
“The way she sees it is it’s to help her brother, but I explained that the money goes to support all people that have got autism like Lewis.
“I’m proud of both of them for what they did, and their school is as well.”
Emma, who accompanied the pair on the day, explained more about the girls’ charity cycle adventure across the island and back.
She said: “They only just got new bikes a couple of weeks beforehand. So it was really a case of get out and go.
“We went with them, following in the car, to help them if needed. Especially on the way to Ettrick Bay, as getting in and out the gates there is tricky. We left the town at 10am and we were back for around lunch time.”