In this contribution, we report a complete set of electro-optic coefficients of iron-doped lithium niobate as function of the composition varying from sub-congruent to near-stoichiometric in a series of four crystals. The concentration of iron is constant for all crystals of the series. The electro-optic measurements of the r(22) and r(c) coefficients were performed on a Senarmont ellipsometric setup while those of r(13) and r(33) were performed on a Mach-Zehnder interferometric setup, by adaptation of the same frequency doubling electro-optic modulation and the MDM methods implemented in both electro-optical arrangements. The corresponding dielectric permittivities epsilon(11) and epsilon(33) as a function of composition were also determined. All electro-optic coefficients reveal a small change with composition, but significant above the experimental error. The nonmonotonous dependences of all electro-optic coefficients are found to be closely linked to their corresponding dielectric permittivities.