The e-retailer, whose billionaire founder and Chief Executive Hiroshi Mikitani has a seat on Lyft's board, recorded the charge because Lyft shares had "fallen significantly" over the July-September period, it said in a statement to the Tokyo Stock Exchange.
Rakuten, the biggest shareholder in Lyft with a stake of more than 11%, is scheduled to announce financial results on Thursday.
The write-down adds to a 28.4 billion yen unrealized loss on Rakuten's Lyft stake for the April-June quarter, with the ride-hailing service locked in a money-burning price war with larger rival Uber Inc in the United States.
At its own earnings presentation last week, Lyft said a growing number of customers were now paying full price for rides, and the improved outlook showed it was on track to be profitable by the end of 2021.
Still, the stock has lost about 40% of its value since the company's initial public offering in March.
(Reporting by Kevin Buckland; Editing by Saumyadeb Chakrabarty)
