This paper reports on the progress of the collaborative research project 'Phonological characteristics of the Japanese lexicon', which was initiated in October 2009. This project investigates the phonetic and phonological aspects of Japanese with main focus on sokuon (geminate obstruents) and accent, with a view to clarifying the main characteristics of the language in comparison with other languages of the world. Regarding sokuon, the project attempts to illuminate the rhythmic structure of Japanese and the perceptual strategies that its native speakers employ, by revealing the linguistic conditions on sokuon in loanwords and their phonetic/phonological basis. Research on accent, on the other hand, studies the prosodic systems of a variety of Japanese dialects in comparison with those of other accent and tone languages in the world such as Korean and Chinese. This paper summarizes the main questions that this project aims to solve as well as some results of the recent research on the two topics.