Predators can trigger antipredator behaviour in their prey, with potential cascading effects on community structure and ecosystem processes. The big-headed turtle (Platysternon megacephalum), a critically endangered species, is a key predator of the freshwater snail (Sulcospira hainanensis) in Hong Kong hill streams. This study examined the antipredator behaviour of S. hainanensis in response to chemical (olfactory) cues from P. megacephalum and dead conspecifics. Snails were exposed for 40 min to one of the four treatments: (1) control (no chemical cues), (2) dead conspecific cue, (3) predator cue, and (4) mixed cues (from both dead snails and turtles). We found that snails exposed to the predator cue exhibited the highest refuge use, whereas snails under the dead conspecific treatment showed increased movement at the start of the experiment, which declined over time. These results suggest that S. hainanensis exhibits cue-specific behaviours, hiding under refuges (analogous to rock crevices in the wild) as the primary defence strategy against turtles, and increased movement for other potential threats. Such behavioural flexibility may reflect adaptation of S. hainanensis to multiple predator types. Our findings demonstrate that P. megacephalum influences the behaviour of S. hainanensis, the dominant grazer in Hong Kong’s hill streams, with a potential cascading effect on habitat and resource use dynamics. Understanding these interactions will advance our knowledge of the ecological roles of Asian freshwater turtles and inform future conservation and environmental education efforts.