Background: Stigma education for nursing students has focused solely on stigma reduction, with studies showing temporary improvements in attitudes. However, nursing education research should also emphasize the importance of critical reflection and self-reflection to enhance attitudes, beliefs, topic comprehension, and learning satisfaction. This study aimed to evaluate the effectiveness of the “This is me” intervention regarding knowledge, attitudes, and communication skills of senior undergraduate nursing students in responding to mental illness-related stigma. Methods: This study employed a psychoeducational intervention for reducing mental illness stigma, using a questionnaire survey to assess pre- and post-intervention effects, with 37 eligible nursing students undergoing clinical training in psychiatric services between 16 May and 15 July 2022. Instruments included sociodemographic and health questions, the MICA-4 scale to evaluate students’ attitudes toward mental illness, the MAKS to measure mental health knowledge, the Empathy Scale (JSPE-S), the Intergroup Anxiety Scale (SS-12), and the Attribution Questionnaire (AQ-27). Results: Most students were female (73.0%) and single (70.3%), with a mean age of around 29 years. After implementing the psychoeducational program, there was a statistically significant increase in overall stigma-related knowledge (MAKS: Z = −1.99, p < 0.05), a decrease in intergroup anxiety (IAS: Z = −3.42, p < 0.05), and reductions in the perceptions of patients as dangerous (AQ27—Dangerousness: Z = −2.399, p < 0.05) and fear (AQ27—Fear: Z = −2.415, p < 0.05). Additionally, there was an improvement in empathy, specifically in Perspective Taking (JSPE: Z = −2.555, p < 0.05). Conclusions: This program may contribute to mental health literacy related to stigma, positively impacting therapeutic relationships and communication with people with mental illness and resulting in more effective care practices.