Let M be a complete Kähler surface and be a symplectic surface which is smoothly immersed in M. Let α be the Kähler angle of in M. In the previous paper Han and Li (JEMS 12:505-527, 2010) 2010, we study the symplectic critical surfaces, which are critical points of the functional L = 1 cos α dμ in the class of symplectic surfaces. In this paper, we calculate the second variation of the functional L and derive some consequences. In particular, we show that, if the scalar curvature of M is positive, is a stable symplectic critical surface with cos α ≥ δ > 0, whose normal bundle admits a holomorphic section X ∈ L 2 ( ), then is holomorphic. We construct symplectic critical surfaces in C 2 . We also prove a Liouville theorem for symplectic critical surfaces in C 2 .