Narrative writing remains a persistent challenge for Indonesian secondary school students, who often struggle with grammar, vocabulary and the development of ideas, while previous studies of animated media have mostly examined writing in general, other text types or other educational levels. This study investigated the difficulties that students experienced in writing narrative texts and examined whether the animated film Frozen was effective in improving the narrative writing ability of Grade XI students at a public senior high school in Padangsidimpuan, North Sumatra, Indonesia. A quantitative pre-experimental one-group pre-test and post-test design was employed with 35 students from one class, who were selected through purposive sampling. Data were collected through a narrative writing test, scored with an analytic rubric of five aspects (content, organisation, vocabulary, grammar and creativity), and a ten-item four-point Likert questionnaire. Because the scores were not normally distributed according to the Shapiro–Wilk test, the pre-test and post-test scores were compared with the Wilcoxon signed-rank test. The mean score rose from 74.29 to 82.00, and 33 of the 35 students improved while none declined (Z = −5.126, p < .001). Grammar was the weakest aspect both before and after the treatment, followed by vocabulary, whereas vocabulary showed the largest gain and organisation the highest post-test mean. Most students also responded positively to the film-based lessons. The findings suggest that a complete animated film, combined with teacher guidance on generic structure, can serve as an effective supporting medium for teaching narrative writing, although grammar requires additional and explicit instructional support.