This paper considers a stability of implicit systems, under which stability every initial-value response of an implicit system does not contain impulses and converges to zero asymptotically. This stability is a generalization of one from the context of descriptor systems, and we applies it to implicit systems that can represent a broader class of systems. We give three necessary and sufficient conditions to this stability: a condition in the Kronecker form, a generalized Lyapunov equation/inequality condition and a certain rank condition of the system pencil. These conditions can be utilized in further research on such as robustness analysis and control systems synthesis based on implicit systems.