A device for controlling pitch of fan blades of a turbine engine including an un-ducted fan, the device including: at least one set of fan blades of adjustable pitch, the set being constrained to rotate with a rotary ring centered on a longitudinal axis and mechanically connected to a turbine rotor, each blade of the set being mounted on a blade root support that is pivotally mounted on the rotary ring; and at least one radial control shaft adjusting pitch of at least two adjacent blades of the set, the control shaft being constrained to rotate with the rotary ring and being configured to pivot about an axis of the shaft, being coupled to the blade root supports of the at least two blades of the set to adjust their pitch via a transmission system including eccentrics connected together by at least one connecting rod.