Affective assessment is one of the components of authentic assessment which requires English teachers to assess the students comprehensively.This study aims to (1) explain the ways in which affective aspects improve students’ English achievement, (2) explain the formulation of an affective assessment for EFL learners using the Rasch model. This research and development approach was employed as the basis to develop rating scale model as an instruments measuring the students’ affective aspects in EFL classroom. The data were analyzed using the Rasch Model. The validity and reliability, in the small–scale field tryout were item reliability 1.00 and person reliability 0.93. Meanwhile, item validity are 0.90 and person validity 0.87 were used in the largescale field one. The results of this study indicate that: (1) there are five affective dimensions or variables developed in this study. They are attitude, motivation, interest, self-concept, and personal value. The five dimensions consist of 24 aspects or sub variables and 35 indicators that become the basis of constracting the 120 item instrument, and as inventory rating scale model. It can be inferred that the affective measuring instrument with the 120 items of statement has a model fit with the data. It means that the model is able to estimate population covariance matrix which is not different from the sample covariance matrix so that the estimation result becomes a basis for generalization.