One of the techniques of teaching English vocabulary to Indonesian learners is by predicting the meaning of the English words from context. But the effectiveness of this technique is very rarely studied. This study aims at finding out the degree of effectiveness of prediction from context. On the basis of a proposed theory that when learners have not had a very large size of references in the long-term memory prediction may fail, it is hypothesized that prediction from context has a low degree of effectiveness. The study makes use of the survey method. It involves 51 subjects. They are the second semester students of the English Department, Faculty of Teacher Training and Education, Widya Mandala Catholic University Surabaya who are randomly sampled from the population that is the second semester students of the English Department. Subjects predict the meaning of 36 English words which are found in 15 reading passages. A criterion of mean score is set to determine the degree of effectiveness of the techniques. The mean score obtained by the subjects is 12. The finding is that the prediction technique has a low degree of effectiveness. The finding supports the proposed theory that when learners, have not had a very large size of references in the long-term memory, prediction may fail