This study aimed to examine the different components of the speaking self-assessment instrument, and the most and least influential factors in the self- assessment instrument affecting Iranian EFL learners’ speaking skill. Finally, utilizing a grounded theory, the model of self -assessment Instrument affecting Iranian EFL learners' speaking skill was designed and validated. Accordingly, 20 language experts and 350 Iranian EFL learners were selected based on convenience sampling. The data were gathered via interviews and questionnaire. The data was analyzed by MAXODA. The findings revealed two broad categories of most influential factors in the self-assessment instrument affecting Iranian EFL learners’ speaking skill are classroom practice concerns EFL teachers’ actions in EFL speaking classrooms and conceptions referring to their beliefs about assessment in general and self-assessment in particular. In addition to teacher assessment, it was also reported using peer assessment can be influential. The participants explained that sometimes comment on their peers’ speaking productions can be conductive. Regarding the assessment techniques, the participants did not provide much information concerning the assessment procedures as no reference was made to any particular assessment techniques or tasks. As far as the least influential factors are concerned, teachers’ formative feedback, and assessment criteria were mentioned, implying that they do not have any significant impact on self- assessment instrument affecting Iranian EFL learners’ speaking skill. Consequently, the model of self-assessment instrument affecting Iranian EFL learners’ speaking skill emerges includes some characteristics and advantages, as well as disadvantages and challenges پرونده مقاله