Just one in 59 rape offences recorded by Dyfed-Powys Police last year resulted in a charge or court summons, new figures show.
And in the area covered by North Wales Police, the proportion was slightly worse, with one in 67 rape offences resulting in a charge or court appearance.
Rape Crisis England and Wales said increased charging rates and access to specialist sexual violence support is vital, as recent data shows rape offences took police forces the longest time to investigate and charge.
Home Office figures show there were 474 rape offences recorded by Dyfed-Powys Police in the year to March. Of them, eight resulted in a charge or summons – accounting for just 1.7 per cent.
The figures show there were 650 rape offences recorded by North Wales Police in the same period, and 10 resulted in a charge or summons – accounting for just 1.5 per cent.
Across England and Wales, 2.6 per cent of rape offences led to a charge or summons, while the overall charge rate for all recorded offences was 6.4 per cent.
Ciara Bergman, chief executive of Rape Crisis, said: “This data reflects what we already know: the criminal justice system must do better for victims and survivors.”
“Those survivors who take the brave steps to report rape and sexual assault do so with the expectation that there will be accountability for the perpetrator.
“With so many survivors being denied their opportunity to seek criminal justice, it’s clear that the system isn’t working. But we need more than a level of commitment; we need to see drastic improvements.”
The Home Office said rape offences that led to a charge or court summons took the longest time to investigate, at an average of 423 days. This is compared with 55 days for violence against the person offences and 28 days for theft offences.
Of the rape offences recorded in Dyfed and Powys, 29.5 per cent were not assigned an outcome as of March, meaning they were still under investigation.
Meanwhile, 36.7 per cent were closed due to evidential difficulties where the suspect was identified, but the victim did not support further action.
In the North Wales area, 37.7 per cent of rape offences were not assigned an outcome as of March, meaning they were still under investigation.