The syntheses and crystal structures and magnetic properties of novel RIn3−xTx (R = Gd,Pr;T = Fe,Co,Mn;x = 0–0.3) intermetallic compounds in rare earth-In-3d transition metal ternary system have been systematically investigated. It reveals that RIn3−xTx crystallizes in cubic AuCu3 type structure with a space group of Pm$\bar 3$m and Z = 1. The 1a and 3c crystal positions are occupied by R and In atoms, respectively. The 3d transition metals substitute partly for In and prefer to occupy the 3c site. The lattice parameters and unit cell volumes decrease with increasing the content of 3d transition metal in RIn3−xTx intermetallic compounds. The magnetic properties of RIn3−xTx are sensitive to T content. With increasing T content, GdIn3−xTx alloys show the paramagnetic, mixture of ferromagnetic and paramagnetic and ferromagnetic behavior. T doping into RIn3 induces the presence of ferromagnetic phase in GdIn3−xTx, which is totally different from those of the pure binary RIn3.