The title compounds [Et4N]2[MS4Cu4(SCN)4(2-pic)4] (M =W 1, Mo 2) have been synthesized by the reaction of (Et4N)2MS4, Cu(SCN) and 2-picoline (2-pic, 2-methylpyridine). Single crystal X-ray diffraction data show that the anion clusters [MS4Cu4(SCN)4(2-pic)4]2-have the planar'open' structure with four Cu atoms in three kinds of coordination modes. Nonlinear optical properties of these two clusters are investigated with a 8 ns pulsed laser at 532 nm. The two clusters exhibit large optical limiting performance, with limiting threshold values of 0.3 J cm-2 for 1, 0.5 J cm-2 for 2, and self-defocusing effects, effective nonlinear refractive index n2 =-6.84×10-12 esu (esu =7.162×1013 m5 v-2) 1 and n2=8.48×10-12 esu 2 respectively. Both compounds show reverse saturable absorption: α2 = 3.1×10-6 m W-1 for 1 and α2=3.2×10-6 m W-1 for 2 in 6.98×10 4 mol dm-3 and 7.44×10-4 mol dm 3 DMF solution respectively. The corresponding effective NLO susceptibilities χ(3) are 6.5×10-8 esu 1 and 8.9×10-8 esu 2 while the corresponding hyperpolarizabilities (γ(1)=9.42×10-32 esu and γ(2)=1.29×10- 31 esu) are also reported.