This study assessed the readability of Igbo language textbook in use in Nigerian secondary schools. Five Igbo Language textbook were evaluated. The study employed an evaluation research design. The study was conducted in South Eastern Geopolitical zone of Nigeria which is predominantly the Igbo tribe of Nigeria. Four hundred secondary school students were used for the study. These students were drawn from five secondary schools (one school from each of the five States of the South Easter zone of Nigeria) that were used for the study. In each school eighty students were drawn for the study (twenty students were drawn from each of the JSS1, JSS2, SS1 and SS2 classes). Data were collected on readability of the textbooks using Igbo Language readability test which are specifically cloze tests of readability. Research questions were answered using percentages while the hypothesis was tested at 95% confidence level using the Chi-Square test of independence. Summary of result reveals that although all the five textbooks were readable their readability indices are below standard expectations of first language textbooks. The study further revealed that readability of the Igbo Language textbooks do not depend significantly on the class levels of the students. Based on these findings the researcher recommends that a readability benchmark should be adopted for all language textbooks in Nigerian schools. Those textbooks that do not meet the minimum benchmark should not be allowed in Nigerian schools.