The tripartite of motivation- affect- cognition indicates the need for more efforts to uncover the complex nature of the interplay of self-efficacy, anxiety as well as motivation. In this study we measured the longitudinal association between adult English a foreign language (EFL) students' self-efficacy and anxiety and the role of ideal self as the predictor of this association. To do this, we applied Latent Growth Curve Modeling (LGCM) to analyze data collected from 367 undergraduate students within a 4 time period during a semester in a course of general English. The findings indicated that while adult students' self-efficacy increased significantly, their level of anxiety decreased during the semester. However, the significance of the intercept and slope variances for both variables implied heterogeneity in the students' growth in self-efficacy and anxiety over the semester. In addition, at the beginning of the semester, the significant negative correlation between adult students' self-efficacy and anxiety was low but during the semester the negative correlation between the two variables turned out to be high. Furthermore, adult students' ideal self could only predict the rate of change in their self-efficacy and anxiety over time, and not their initial level. The qualitative data provided further insights into adult learners' change in their states of self-efficacy and anxiety detected primarily by the LGCM phase.