The police say they are satisfied no offence was committed by New Zealand First over the returns of party donations in 2007.
ACT Party leader Rodney Hide had complained to the police that an $80,000 payment from the Spencer Trust was not declared.
In their decision, released on Tuesday 4 November, the police say they are satisfied no offence was committed and they are taking no further action.
Two weeks ago, the Electoral Commission cleared the party over the same return, saying it had committed no offence, but withheld its decision due to the pending police investigation.
The Serious Fraud Office also found the party had not committed any fraud.
Mr Hide says he is pretty amazed at the decision but he expected such an outcome because he believes the inquiry was not independent.
Despite being cleared by the police, New Zealand First leader Winston Peters says it is not acceptable they waited until just days before the election to release their decision.
Mr Peters told Checkpoint he thought the police would have made their announcement a lot sooner.
"To leave it until almost three days out from the election, and then make a decision on information, allegations which were baseless from the start, simply's not good enough. They know how important this issue in terms of the public's decision making process and leaving it this late is simply not acceptable."
He says the allegations were designed to hurt his party's chances at the election.
National leader John Key says Mr Peters was still found to have misled parliament and he is still ruling him out of any coalition.