The crystal structure and luminescence properties of hydrothermally grown crystals of Cs3EuSi6O15 are reported. The structure consists of loop-branched vierer double chains of silicate with four-, six-, and eight-membered rings, which are connected via 10-membered rings at their interfaces to form a 3-D silicate framework. The six-coordinate europium atoms are located at sites between six-membered silicate rings. This Cs, Eu silicate is the second example of 3-D silicate framework with Si:O = 2:5, which contains only tertiary [SiU4] tetrahedra. The sharp peaks in the emission spectrum are assigned, and the lifetime measurements confirm the presence of one local Eu3+ environment. Crystal data: monoclinic, space group P21/n, a = 7.1664(1) Å, b = 28.4756(6) Å, c = 8.5418(2) Å, β= 104.976(1)°, V = 1683.89(7) Å 3, and Z = 4.