ENRecently, there has been an increasing need to develop mental toughness of students who participate in sport, in order to improve their adaptation not only during sporting activities but also in other contexts. Developing mental toughness skills among sport school students is one of the main ways to ensure their psychological well-being, and therefore research in this area is of great importance. However, there is currently a lack of adapted validity measures that consider sociocultural factors to assess their psychological skills, namely mental toughness. For this purpose, it is necessary to adapt and validate a modern, useful measure of psychological resilience skills. Therefore, the aim of this paper is to conduct an adaptation of the Psychological Performance Inventory-Alternative (PPI-A) for sport school students. The participants of the study were 378 basketball sport school students aged 15-18 years from different Lithuanian basketball sport schools. Confirmatory factor analysis (CFA) was conducted using Jamovi software. Pearson correlation coefficients and average variance extracted were calculated using Jamovi software and Excel program.These indicators were used to check the convergent and discriminant validity of the questionnaire. Reliability of the questionnaire was checked using Cronbach's alpha and McDonald's omega. Structural equation modelling showed an acceptable fit of the four-factor PPIA model. Validity and reliability analyses revealed a good level of internal consistency between the factors. Given the appropriate psychometric properties, the Lithuanian version of the Psychological Performance Inventory-Alternative (PPI-A) can be used in studies aimed at better understanding of mental toughness among sport school students. Further research on the structure of the instrument is also warranted in order to validate the questionnaire for other samples. Keywords: mental toughness, psychological performance, validation, adaptation, sport schools, students. [From the publication]