A thesis is a formal academic writing; however, since nowadays communication tends to become more informal, some theses may also use informality features. This study aims at analyzing the undergraduate thesis abstracts from the years of 1992, 1996, 2000, 2004, 2008, 2012, and 2016 of Indonesian EFL students. This study found that the thesis abstracts contained eight types of informality features: first-person pronouns, second-person pronouns, sentence-initial conjunctions/conjunctive adverbs, sentence-final prepositions, run-on sentences/expressions, sentence fragments, contractions, and direct questions. From those eight features, four of them have constantly appeared over time. The statistical calculation shows a negative correlation between the years and these four features: the first-person pronouns, the sentence-initial conjunctions/conjunctive adverbs, the run-on sentences/expressions, and the sentence fragments. This means that the use of informality features has decreased overtime. This could signify that there has been an improvement in the teaching and learning process or that the EFL learners have become more conservative in their academic writing.