KOI-3503 is a Sun-like F-type star (about 0.86 solar masses, 6,001 K, 1.25 solar radii), 887 light-years from Earth. KOI-3503 b is a 9.2-Earth-mass planet, with an orbital period of 21.2 days, and an equilibrium temperature near 785 K, discovered in 2021 via transit. KOI-3503 c is a 10.4-Earth-mass planet, with an orbital period of 31.8 days, and an equilibrium temperature near 686 K, discovered in 2021 via transit. The planet was found when it crossed the face of its star, producing periodic dips in brightness that reveal its size and orbital period to space-based photometry.