This study re-evaluated the weak-form efficiency of the Korean securities market in line with the international trend of re-examining capital market weak-form efficiency—derived from the random walk hypothesis—through nonlinearity testing methods. In particular, Taylor's nonlinear variance-ratio model, which serves as the foundation among nonlinearity testing methods, was employed. The research results revealed that the daily stock return series of the Korean stock market exhibits stochastic transient fluctuations in the long run, indicating that it is a market where profit-seeking opportunities may exist. The findings of this study will be useful in replacing the capital market system theory, which has been developed based on linear stochastic dynamic mechanisms, with nonlinear stochastic models or linear deterministic models.