Aposematic animals advertise their unprofitability to potential predators via morphological and behavioral signals. Strong signals are detectable and memorable for the predators, and such signals would therefore be expected to be most effective. However, many apparently well-defended animals do not have very conspicuous signals. To better understand this paradoxical phenomenon, I compared intra-individual variation in an immobile aposematic behavior of the newt Cynops pyrrhogaster under different thermal gradients, using 40 animals from four populations. I found a negative relationship between ambient temperature and the frequency of performing this behavior, independent of body size. Newts kept in low temperature conditions showed a stronger tendency to display the immobile aposematic behavior than those in high temperature conditions, indicating that this behavior in the newt is temperature-dependent. However, interpopulational comparison of thermal thresholds governing the decision to flee or remain immobile as an antipredator strategy suggested that the effect of temperature might not be responsible for interpopulational variation in the immobile aposematic behavior of the newt.