Fuel injection control system

To provide a fuel injection control system which properly sets a limit value of an air-fuel ratio feedback correction value, thereby making a good air-fuel ratio feedback control possible. While a variation rate of an output value of an oxygen sensor (32) is changed from the positive to the negative or from the negative to the positive predetermined times after a power source of a vehicle is turned on, a control unit (C) sets a first limit range (L1) for an air-fuel ratio feedback correction factor (K02) as an upper/lower limit value which have a predetermined upper/lower width, in which the output value of the oxygen sensor (32) detected in a stoicshiometric air-fuel ratio state is a reference value (B1), and which is allowed to be used for calculating a correction injection quantity (T1). After a variation rate of the output value of the oxygen sensor (32) is changed from the positive to the negative or from the negative to the positive predetermined times, the air-fuel ratio feedback correction factor (K02) that is calculated when the variation rate is changed the predetermined times is regarded as a reference value (B2), and a second limit range (L2) which has a predetermined upper/lower width from the reference value (B2) and is narrower than the first limit range (L1) is set.