The nominee, Seyen Mohsen Tasalloti, won the backing of only 77 out of 254 parliamentarians present during the vote.
Tasalloti, a veteran of the petrochemicals industry, had been the target of rumors over his personal life and alleged fortune.
Lawmakers rejected Ahmadinejad's first nominee in August.
His second nominee pulled out of the race earlier this month before lawmakers were due to cast their votes.
RFE/RL Iran Report
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