A marine vessel electric propulsion system comprising: an electric motor; a propulsive force generator to be driven by the electric motor to generate a propulsive force; an operator to be operated by a user to adjust a power output of the electric motor; and a controller configured or programmed to control the power output of the electric motor based on an operation of the operator, and to change a power output gain characteristic of the electric motor with respect to an operation amount of the operator in response to a gain change command, and to control the power output of the electric motor based on any one of a plurality of gain characteristics in response to the gain change command; characterised in that the plurality of gain characteristics include a first gain characteristic (L1, L11, L12, L13, L14) and a second gain characteristic (L2, L21, L22, L23, L24) that has a smaller gain than the first gain characteristic (L1, L11, L12, L13, L14); and the first gain characteristic (L1, L11, L12, L13, L14) includes a lower limit and an upper limit of an operation range of the operator that respectively correspond to a first power output value of the electric motor and a second power output value of the electric motor that is greater than the first power output value; and the second gain characteristic (L2, L21, L22, L23, L24) is defined such that the lower limit and the upper limit of the operation range of the operator respectively correspond to the first power output value of the electric motor and a third power output value of the electric motor that is greater than the first power output value and smaller than the second power output value. an electric motor; a propulsive force generator to be driven by the electric motor to generate a propulsive force; an operator to be operated by a user to adjust a power output of the electric motor; and a controller configured or programmed to control the power output of the electric motor based on an operation of the operator, and to change a power output gain characteristic of the electric motor with respect to an operation amount of the operator in response to a gain change command, and to control the power output of the electric motor based on any one of a plurality of gain characteristics in response to the gain change command; characterised in that the plurality of gain characteristics include a first gain characteristic (L1, L11, L12, L13, L14) and a second gain characteristic (L2, L21, L22, L23, L24) that has a smaller gain than the first gain characteristic (L1, L11, L12, L13, L14); and the first gain characteristic (L1, L11, L12, L13, L14) includes a lower limit and an upper limit of an operation range of the operator that respectively correspond to a first power output value of the electric motor and a second power output value of the electric motor that is greater than the first power output value; and the second gain characteristic (L2, L21, L22, L23, L24) is defined such that the lower limit and the upper limit of the operation range of the operator respectively correspond to the first power output value of the electric motor and a third power output value of the electric motor that is greater than the first power output value and smaller than the second power output value.