Machine for filling bags with predefined quantities of loose products, the machine extending in a longitudinal direction (X-X) of movement of the bags from an upstream inlet to a downstream outlet, there being defined a sense of movement concordant with the advancing movement of the bags from upstream to downstream and a sense of movement opposite to the preceding sense in the longitudinal direction (X-X), the machine comprising: - a station (A,F) for feeding, to a single pick-up position, a bag oriented with its mouth extending in a transverse direction (Y-Y) perpendicular to the longitudinal direction (X-X) of advancing movement; - at least a first filling station and a second filling station of filling stations (R1,R2,Rn) for filling a respective bag, which are arranged in succession along the longitudinal direction (X-X) of movement of the bags, downstream of the pick-up position, each filling station (R1,R2,Rn) being associated with respective gripping means for gripping the bag; said pick-up position and at least two filling stations (R1,R2,Rn) being arranged at a predefined and identical relative distance from one another, which corresponds to a step between adjacent stations in the longitudinal direction (X-X); - transport means (100,1100) for transporting the bags from one station to the other station, which are movable in both senses (V1,V2) of the longitudinal direction (X-X) and are provided with pairs of gripping means for gripping a bag, the gripping means of a pair being arranged opposite each other in the transverse direction (Y-Y); the machine being configured so that the said transport means (100,110) perform single translation movements, each with a displacement equal to one step in the sense opposite to the sense of advancing movement of the bags in the longitudinal direction (X-X) and with a displacement equal to a number of steps which is equal to the number of filling stations (R1,R2,Rn) in the sense concordant with the advancing movement of the bags in the longitudinal direction (X-X), wherein said pairs of gripping means (110a, 110b, 110c, 110d) for gripping a bag comprise a number of pairs at least equal to twice the number of filling stations (R1,R2,Rn), each pair of gripping means being arranged at a distance of one step in the longitudinal direction (X-X) from the pair/s of bag gripping means adjacent thereto. - a station (A,F) for feeding, to a single pick-up position, a bag oriented with its mouth extending in a transverse direction (Y-Y) perpendicular to the longitudinal direction (X-X) of advancing movement; - at least a first filling station and a second filling station of filling stations (R1,R2,Rn) for filling a respective bag, which are arranged in succession along the longitudinal direction (X-X) of movement of the bags, downstream of the pick-up position, each filling station (R1,R2,Rn) being associated with respective gripping means for gripping the bag; said pick-up position and at least two filling stations (R1,R2,Rn) being arranged at a predefined and identical relative distance from one another, which corresponds to a step between adjacent stations in the longitudinal direction (X-X); - transport means (100,1100) for transporting the bags from one station to the other station, which are movable in both senses (V1,V2) of the longitudinal direction (X-X) and are provided with pairs of gripping means for gripping a bag, the gripping means of a pair being arranged opposite each other in the transverse direction (Y-Y); the machine being configured so that the said transport means (100,110) perform single translation movements, each with a displacement equal to one step in the sense opposite to the sense of advancing movement of the bags in the longitudinal direction (X-X) and with a displacement equal to a number of steps which is equal to the number of filling stations (R1,R2,Rn) in the sense concordant with the advancing movement of the bags in the longitudinal direction (X-X), wherein said pairs of gripping means (110a, 110b, 110c, 110d) for gripping a bag comprise a number of pairs at least equal to twice the number of filling stations (R1,R2,Rn), each pair of gripping means being arranged at a distance of one step in the longitudinal direction (X-X) from the pair/s of bag gripping means adjacent thereto.