Intraneuronal deposition containing $alpha$-synuclein is implicated in the pathogenesis of synuclein-opathies including Parkinsons disease (PD). Although it has been demonstrated that cytoplas-mic inclusions of wild type $alpha$-synuclein are observed in the brain of PD patients and that $alpha$-synuclein mutations such as A30P and A53T accelerate aggregate formation, the exact mech-anism by which $alpha$-synuclein forms insoluble aggregates is still controversial. In the present study, to understand the possible involvement of tissue transglutaminase (tTG) in aggregate formation of $alpha$-synuclein, SH-SY5Y cell lines stably expressing wild type or mutant (A30P or A53T) $alpha$-synuclein were created and aggregate formation of $alpha$-synuclein was observed upon activation of tTG. The data demonstrated that $alpha$-synuclein negligibly interacted with tTG and that activation of tTG did not result in the aggregate formation of $alpha$-synuclein in SH-SY5Y cells overexpressing either wild type or mutant $alpha$-synuclein. In addition, $alpha$-synuclein was not modi-fied by activated tTG in situ. These data suggest that tTG is unlikely to be a contributing factor to the formation of aggregates of $alpha$-synuclein in a stable cell model.