Following Nation’ (2009) proposal of 40-50 empty spaces as an optimum length of a cloze test, this study examined whether this length would work according to proficiency level. Three cloze tests, adjusted for each proficiency level, were developed by the researcher for the use at beginning, intermediate and advanced levels. The cloze tests measured participants’ reading comprehension and included 40, 45 and 50 empty spaces for the beginning, intermediate and advanced levels respectively. Problematic items of each cloze test were identified over several pilot studies. Then they were administered to three groups of L1 Persian EFL learners at the beginning (56), intermediate (43), and advanced (41) levels. Results of the study suggest that an optimum length of a cloze test could vary according to the proficiency level. While the test could be long (including 50 empty spaces) and reliable at the advanced level, a shorter length of the test including 20-25 empty spaces could be more reliable at the beginning and intermediate levels.