The main focus of this study was to examine the relationship between Library instructions and undergraduate students’ effective use of Ignatius Ajuru University of Education Library in Rivers State, Nigeria, Survey research method was used. The population of the study was 85 library science students in Ignatius Ajuru University of Education in Rivers State. Census technique was used where all the 85 library science students were used as respondents. The instrument for this study was a questionnaire titled Library Instructions and Undergraduate Students’ Effective Use of Ignatius Ajuru University of Education Library Questionnaire (LIUSEUIAUELQ). The instrument was given for face validation to two validates from the Library and Information Science unit of Ignatius Ajuru University of Education Libraries in Rivers State. The reliability of the instrument was determined using test-retest technique and data was analysed using Cronbach Alpha statistics which yielded a coefficient of 87. The researcher administered questionnaires to the respondents and retrieved after two days. Eight-five (85) copies of the questionnaire were distributed to questionnaire the respondents and successfully retrieved 81 copies giving ninety-five percent (95%) return rate. Linear Regression statistics was used to analyze data. The finding revealed that there is a significant relationship between Library orientation, Library guide and undergraduate students’ effective use of Ignatius Ajuru University of Education Library in Rivers State, Nigeria. The researcher therefore recommended that the university authority should make library orientation compulsory for all undergraduate students and provide adequate library guide to help them in their academic work, enhance reading culture among them, and ensure undergraduate students’ effective use of Library.