The present study aimed to examine the relationship between assertiveness and academic achievement motivation of adolescent students in selected secondary schools of Harari Peoples Regional State among a sample of 332 (145 males and 187 females). Data were collected through the twenty-four-item of academic achievement motivation (AAM) inventory with four-point rating scale that was adapted from previous versions and scales for assessing Assertive Behaviour a thirty-item instrument with six-point rating scale ranging from (+3, very characteristic of me to -3, very uncharacteristic of me) that was adapted from previous research. Data were analyzed employing a blend of both descriptive and inferential statistical methods that were successively conducted to examine the level of assertive behavior employing one-sample mean test and combined effects of independent variables on dependent variable (academic achievement motivation) were made employing regression analysis. Findings indicated that: Harari peoples regional state adolescent students participated in present study were scored low on the assertiveness; male adolescents were found to be better in their levels of assertiveness than their female adolescent counterparts. With pertaining to the relationship between assertiveness and academic achievement motivation was concerned, there was a statistically significant positive relationship between them. Additionally, it was found that there was a statistically significant positive relationship between parental educational status and assertiveness. Unlike assertiveness and parental educational status, sex appeared to be a less important factor in explaining adolescents' academic achievement motivation. Attempts were made to explain findings within the existing ecological and socio-cultural practices of the study area. Recommendations were also suggested as to how to properly address the gaps noted in this research.