This study investigates the development of vocabulary by means of one of the least investigated methods to language teaching, Suggestopedia/Reservopedia. To that end, the researcher, under the light of her training by the developer of the method Georgi Lozanov, adapted the authorized coursebook used in the department to the method and modified the teaching according to the laws, principles and means of Suggestopedia/Reservopedia. The data were collected from a sample of 45 Turkish students who were attending the preparatory classes at the Abant Izzet Baysal University (AIBU) in Bolu, Türkiye, in the Fall semester of the 2008-2009 academic year. The participants were between the ages of 17-20 learning English as a foreign language at elementary level. To investigate the effects of Suggestopedia/Reservopedia on students' vocabulary achievement, two groups were randomly formed: one was the experimental group which would learn vocabulary using Suggestopedia/Reservopedia, the other would be the control group which would be subjected to vocabulary teaching in the non-Suggestopedic/Reservopedic way. In the selection of the vocabulary items to be taught, one criterion that was followed was determining the words students would learn. In order to maximize the benefit for both groups, three word count studies were consulted. They were Academic Word List, General Word List, and University Word List. Thus, the majority of the words were chosen on the basis of those lists. Considering that students would be tested on the vocabulary items in their book, the vocabulary words not included in those lists, but included in the coursebook were also included in vocabulary teaching. Statistical analyses revealed that the students in the experimental group significantly outperformed those in the control group in the vocabulary tests. With regard to long-term retention of the vocabulary words, the results also pointed out that Suggestopedic/Reservopedic students were able to remember them better compared to the control group. Thus, it was concluded that Suggestopedic vocabulary teaching had a significant effect on vocabulary learning.