This paper analyzes the fluctuation and alternation of two active participle forms in Uilta: one is formed by the suffixes -si/-či(n), and the other is formed by the suffixes +ri/-xA(n), which is more productive than the former. This alternation between -si/-či(n) and +ri/-xA(n) usually results in changes in meaning. While the -si/-či(n) form conveys continuous and iterative aspects, the +ri/-xA(n) form contrastively conveys perfective, resultative, and prospective aspects. The fluctuation of forms, however, sometimes does not make any aspectual differences. This means that the participle forms formed by suffixes -si/-či(n) are regularized to the +ri/-xA (n) form. which has also been observed in neighboring languages such as Nanai and Ulcha.