Objective: Metacognitive models posit that beliefs about thoughts and memories influence the development of posttraumatic stress disorder (PTSD) symptoms following traumatic events. This study examined the relationship of beliefs about memory with peritraumatic experiences in the development of PTSD symptoms following the Canterbury earthquakes and Queensland floods. Method: A convenience sample of individuals affected by these disasters (N = 662) was given questionnaires measuring peritraumatic distress and dissociation, beliefs about memory, and PTSD symptoms. Results: The results showed that individuals with a high level of peritraumatic distress and dissociation or high level of positive or negative beliefs about memory reported increased PTSD symptoms compared to those with a low level of the respective variable. Furthermore, peritraumatic distress and dissociation interacted with negative beliefs about memory. The difference in PTSD symptoms for those with a high compared to low level of peritraumatic distress and dissociation was elevated when individuals also reported a high level of negative beliefs about memory. This difference was diminished for individuals who reported a low level of negative beliefs about memory. Conclusions: These findings suggest that beliefs about memory may moderate the effects of peritraumatic distress and dissociation on PTSD symptoms following a natural disaster. Given that metacognitive beliefs are a modifiable risk factor, future research is warranted to consider their potential causal effects on PTSD outcomes, particularly for individuals with severe peritraumatic experiences.