Mental contamination (i.e., feelings of dirtiness in the absence of contact with a contaminant) is a potentially important yet understudied factor in posttraumatic psychopathology, particularly for survivors of sexual trauma. Mental contamination has been linked to PTSD symptom severity, negative affect, and coping cross-sectionally and in lab-based paradigms, but research has yet to assess these relationships in ecological contexts. The present study extends previous cross-sectional findings by modelling relationships between mental contamination and posttraumatic psychopathology, emotions, and coping both within-day and from one day to the next. Forty-two female sexual trauma survivors completed twice-daily assessments of mental contamination, PTSD symptoms, negative emotions, and avoidant/approach coping via a smartphone app. Daily averages and intraindividual changes in mental contamination scores were linked with PTSD symptoms at the same timepoint. Mental contamination also significantly predicted several specific avoidant coping strategies at later timepoints in addition to concurrent links. Unexpectedly, several negative emotions exhibited positive links with concurrent mental contamination but were negatively linked to later mental contamination. Exploratory analyses identified a significant interaction whereby elevated morning negative affect predicted evening reductions in mental contamination, but only for individuals also high in morning PTSD symptoms. Lastly, prevalence of reported baseline mental contamination was much higher in the present study compared to prior research. Clinical relevance and future recommendations for ecological research in trauma-related mental contamination is discussed.