SHANGHAI, July 15 (Reuters) - China's central bank left a medium-term rate unchanged as expected on Monday when rolling over maturing medium-term loans.

The People's Bank of China (PBOC) said it was keeping the rate on 100 billion yuan ($13.8 billion) in one-year medium-term lending facility (MLF) loans to some financial institutions unchanged at 2.50% from the previous operation.

In a Reuters poll of 35 market watchers conducted last week, only one respondent expected the PBOC to deliver a marginal interest rate reduction. A vast majority of them predicted a partial roll-over.

With 103 billion yuan in MLF loans set to expire this month, the operation resulted in a net 3 billion yuan fund withdrawal from the banking system.

The central bank also injected 129 billion yuan through seven-day reverse repos while keeping borrowing costs unchanged at 1.80%, it said in an online statement.

($1 = 7.2500 yuan)

(Reporting by Shanghai Newsroom; Editing by Tom Hogue)