Purpose: To evaluate the effect of preoperative information based on written documents on anxiety levels and the family-centered care of parents of pediatric patients who had ambulatory surgery. Design and methods: It is a randomized controlled study. Parents were randomly divided into two groups as intervention (n = 30) and control (n = 30). Parents in the intervention group were given written document and verbal information the day before the surgery. A brochure was prepared in accordance with the verbal information describing the perioperative process as a written document. The control group was given only verbal information. Parental State Anxiety Inventory (SAI) and Family Centered Care Assessment Scale (FCCAS) were assessed before and within 1–2 h after surgery, with verbal information based on written documentation. Data were evaluated with Student's t-test for dependent and independent groups and mixed design ANOVA test for time×group interaction. Partial eta square (η2) was calculated for the effect size. Results: There was a significant difference between the post-intervention pretest and posttest SAI and FCCAS scores of the parents in the intervention and control groups (p < 0.05). Time group interactions anxiety and family-centered care (p < 0.001) scores had a significant and large effect size. Conclusion: Verbal information supported by written documentation before pediatric ambulatory surgery can reduce parental SAI and increase parental FCCAS more than standard care. Practice implications: Providing written document-based information to parents before surgery may be beneficial in reducing SAI and increasing FCCAS. The trial was registered in ClinicalTrials.gov (identifier: NCT05668416).