The Treasurer of the Scottish National Party, Colin Beattie, has been released without charge pending further investigation.
It follows the arrest of a 71-year-old earlier in the day in connection with an investigation into the party's finances.
Police Scotland say a report is now to be sent to the Crown Office and the Procurator Fiscal.
The arrest of Mr Beattie, who also serves as an MSP for Midlothian North and Musselburgh, is the second in relation to an investigation into how more than £600,000 in donations to the party earmarked for an independence referendum had been used.
Former party chief executive Peter Murrell was arrested earlier this month and questioned for more than 11 hours before being released without charge “pending further investigation.”
Mr Murrell is the husband of former first minister Nicola Sturgeon.
The new First Minister Humza Yousaf has ordered a review of "transparency and good governance" in the party.