DyAg 2 Si 2 has been studied by powder neutron diffraction. The magnetic phase transition T t = 4.3 K and the Néel temperature T N = 10.3 K have been determined by the temperature dependences of the intensities of the (½0½) and (0⅓1 magnetic peaks. Between T l and T N , the magnetic structure is a collinear antiferromagnet with ↑ ↓↓ ↑ ↓↓ , in which two kinds of Dy moment aligned along the a-axis, μ 1 = 6.7μ B and μ 2 = 3.4μ B (at 7 K) are coupled antiferromagnetically with the sequence ↑ ↓↓ ↑ ↓↓ along the b-axis. Below T t , the two propagation vectors k 2 = (½0½) and k 1 give a non-collinear antiferromagnet with two kinds of Dy moment of μ 1 = 8.9μ B and μ 2 = 7.5μ B (at 1.7 K).