Pre-tax profits dropped to £49m from £53.5m in 2014.
But the Cardiff-based society - the largest in Wales - said it had helped 3,500 first-time buyers onto the housing ladder, up by 1,200 on the previous year.
It also warned 67 workers at its Nemo secured loans business that they were at risk of redundancy.
It has been trying to offload Nemo and said it would no longer take on any new customers.
However, the building society said it believed it could find jobs for many of the staff within its 1,000 strong workforce.
Meanwhile, Principality, which is the sixth biggest society UK-wide, said mortgage lending to home-buyers had passed the £5bn mark for the first time.
Graeme Yorston, group chief executive, said it had been "another strong 12 months".
He said the society would continue to respond to technological demands, which have included rolling out mortgage interviews on Skype and online appointment booking.
Underlying profit was £57.8m, up from £51.9m.
This included dealing with one-off issues like stopping new lending from its subsidiary Nemo, which provides secure loans on properties.
There has been speculation over recent years that Principality would look to sell this part of its business.
It will continue to manage accounts it currently has.
Mr Yorston said although Nemo had made a £14m profit, it did not want to "increase our participation in this market".
Looking ahead at economic prospects, he said he did not expect to see any rise in the official Bank of England base rate until 2017 and "when it does it is likely to be modest".
Principality Building Society has announced a dip in its profits for 2015, after a record the year before.