The charity has been using the tool for a month on two awareness and fundraising campaigns, 'Voices' and 'Biggest Animal Rescue', and has seen an uplift in response rates.
It now plans to use Upcast in two forthcoming campaigns intended to support rehoming Staffordshire bull terriers and the RSPCA's virtual gift catalogue.
According to RSPCA web analyst Joe Wilson, Facebook's own ad interface is "pretty basic and only really suitable for small, simple campaigns" targeted at three or four defined demographic groups.
Upcast is a more automated system, allowing the RSPCA to create thousands of variants of its ads targeted to a much wider spread of groups of people defined by locations, interests, relationship status and age.
I Spy Labs is the technology partner of digital marketing agency I Spy, which handles the RSPCA's PPC account.