[en] Anomalous transport properties of 40-nm-thick single-crystal Bi(111) films grown on Si(111)-7 × 7 substrates is investigated. The magnetoresistance (MR) of the films in perpendicular magnetic field shows a regular positive behavior in the temperature range 2–300K, the MR in parallel field (B_||) displays a series of interesting features. Specifically, we observe a change of the MR (B_||) behavior from positive to negative when the temperature is below 10K. In the range 10–170 K, the MR (B_||) is negative in the investigated field of 9T. When T > 170 K, a positive MR appears in the high field regime. The low temperature MR(B_||) behavior in the parallel field can be understood by the competition between weak localization and weak anti-localization (WAL). Furthermore, our results suggest that the WAL is dominated by the interface carriers