System for estimating the slope (θ) of a pedal-assisted bicycle comprising an electric motor connected to a wheel of the bicycle and one or more sensors/modules configured to generate signals representative of quantities relative to the bicycle, the system comprising: - a sensor for detecting the longitudinal speed (V x) of the bicycle, said sensor being configured to generate a signal representative of the longitudinal speed of the bicycle; - an inertial measurement unit configured to measure the longitudinal (a x), lateral (a y) and vertical (a z) accelerations and the angular velocities of roll (ω x), pitch (ω y) and yaw (ω z) of the bicycle and configured to generate signals representative of the longitudinal, lateral and vertical accelerations of the bicycle and of the angular velocities of roll, pitch and yaw of the bicycle; - a module for estimating the slope (θ) of the bicycle comprising: • an extended Kalman filter configured to recursively calculate a gain (K k) of the Kalman filter based on said signals representative of the longitudinal speed (V x), the longitudinal (a x), lateral (a y) and vertical (a z) accelerations and on the angular velocities of roll (ω x), pitch (ω y) and yaw (ω z) of the bicycle and configured to estimate said slope (θ) of the bicycle based on said gain (K k) of the Kalman filter; • a module for determining correction parameters adapted to modify said gain (K k) of the Kalman filter based on one or more of said signals representative of the quantities of the bicycle which affect said estimation of the inclination (θ) performed by the extended Kalman filter; wherein the module for determining correcting parameters (S, T) of the gain (K k) of the Kalman filter is configured to determine a first and a second correction coefficient which are such that the gain (K k) of the Kalman filter decreases as the difference between the first correction coefficient and the second correction coefficient increases, and increases as the difference between the second correction coefficient and the first correction coefficient increases. - a sensor for detecting the longitudinal speed (V x) of the bicycle, said sensor being configured to generate a signal representative of the longitudinal speed of the bicycle; - an inertial measurement unit configured to measure the longitudinal (a x), lateral (a y) and vertical (a z) accelerations and the angular velocities of roll (ω x), pitch (ω y) and yaw (ω z) of the bicycle and configured to generate signals representative of the longitudinal, lateral and vertical accelerations of the bicycle and of the angular velocities of roll, pitch and yaw of the bicycle; - a module for estimating the slope (θ) of the bicycle comprising: • an extended Kalman filter configured to recursively calculate a gain (K k) of the Kalman filter based on said signals representative of the longitudinal speed (V x), the longitudinal (a x), lateral (a y) and vertical (a z) accelerations and on the angular velocities of roll (ω x), pitch (ω y) and yaw (ω z) of the bicycle and configured to estimate said slope (θ) of the bicycle based on said gain (K k) of the Kalman filter; • a module for determining correction parameters adapted to modify said gain (K k) of the Kalman filter based on one or more of said signals representative of the quantities of the bicycle which affect said estimation of the inclination (θ) performed by the extended Kalman filter; • an extended Kalman filter configured to recursively calculate a gain (K k) of the Kalman filter based on said signals representative of the longitudinal speed (V x), the longitudinal (a x), lateral (a y) and vertical (a z) accelerations and on the angular velocities of roll (ω x), pitch (ω y) and yaw (ω z) of the bicycle and configured to estimate said slope (θ) of the bicycle based on said gain (K k) of the Kalman filter; • a module for determining correction parameters adapted to modify said gain (K k) of the Kalman filter based on one or more of said signals representative of the quantities of the bicycle which affect said estimation of the inclination (θ) performed by the extended Kalman filter;