Background: Expressive writing (EW: a personal form of writing about emotional distress, without regard to writing conventions) can improve physical and mental health. The present study investigated whether EW can reduce pathological skin-picking. In addition, the effects of two modalities of writing were contrasted with each other: computer vs. paper/pencil. Method: A total of 132 females with self-reported pathological skin-picking participated in a two-week intervention. They either carried out six EW sessions or wrote about six abstract paintings (control condition), using either paper/pencil or a computer. Before and after each session, participants rated their affective state and the urge to pick their skin via a smartphone application. Questionnaires for assessing skin-picking severity were completed before and after the two-week intervention. Results: The urge for skin-picking decreased directly after a writing session. The reduction was more pronounced in participants of the EW group, who also experienced reduced tension and increased feelings of relief at the end of a writing session. EW also reduced the severity of focused skin-picking after the two-week intervention. The writing modality had no differential effect on skin-picking symptoms. Conclusions: This study identified beneficial effects of EW on pathological skin-picking. A future study could investigate EW as a potential tool in the context of (online) psychotherapy for skin-picking disorder.