The objective of this study assesses the impact of Afaan Oromo dialectal variation on teaching learning process of the language at two selected tertiary levels, Madda Walabuu University (MWU) and Robe Teachers College (RTC).To achieve this objective, the focuses are given, particularly to the awareness, tolerance and experience that the teachers have on dialectal variation of the language, the types of dialectal variation of the student, the attitude of the respondents towards the standardization of the language and factors that lead instructors to the linguistic bias. The subjects of the study are the sample of students and instructors of the selected institutions. The data were gathered from a total of 48 respondents, 39 students and 9 instructors through interview, questionnaire and document analysis, and the collected data are analyzed using quantitative methods. Then the following results have been obtained: the instructors’ knowledge, awareness and tolerance about dialectal variation of the language are imperfect. The majority of the students and the instructors have positive attitude towards their dialect to become a standardized dialect. Lack of experience in teaching, high level of education, learning linguistic course(s), particularly dialectology leads the instructors to linguistic bias. Linguistic variations like lexical morphological and syntactic are the major dialectal variation of the language that affects the academic achievement of the students Therefore, hiring experienced instructors in the institution, enhancing the instructors’ educational level, incarnating linguistics course (s) in the program of teachers and student training are recommended as the solution of the addressed problems