HONG KONG, Nov 30 (Reuters) - Hong Kong's Exchange Fund, which is used to back the Hong Kong dollar, posted an investment loss of HK$100.1 billion ($12.82 billion) in the third quarter, the Hong Kong Monetary Authority (HKMA) said on Wednesday.

The Exchange fund recorded an investment loss of HK$265.5 billion in the Jan-Sept period this year.

The HKMA is the key manager of the Exchange Fund, which is under the control of the financial secretary and invests in equities, bonds, foreign exchange and other securities and assets. ($1 = 7.8111 Hong Kong dollars) (Reporting by Twinnie Siu and Donny Kwok; Editing by Kim Coghill)