A novel scheme of an ultralow relative intensity noise (RIN) broadband source module employing a double pumped backward (DPB) Er-doped superfluorescence fiber source (EDSFS) and a semiconductor optical amplifier for interferometric fiber optic gyroscopes (IFOGs) is proposed. With optimized parameters, the optimal twin-peak output profile of the source is obtained. The effective optical spectrum width of the source is 38.6 nm, and the output power is about 12.5 mW. Compared with the DPB EDSFS with a similar spectrum, the ultralow RIN broadband source proposed demonstrates a lower RIN of about 8.4 dB. A high-precision IFOG utilizing the ultralow RIN broadband source is set up, and the performance of the IFOG is experimentally studied. An angle random walk coefficient of 6.93×10-5o/h1/2 is demonstrated, which is reduced by about 31.5% compared with the same IFOG system utilizing conventional DPB EDSFS with a similar spectrum profile. The ultralow RIN broadband source module proposed is quite feasible for high-precision IFOGs used in strategic-grade navigation systems and satellites.