We investigated phenology of the invasive Aedes japonicus japonicus at Lake Balaton for two years. From July of 2017, the relative abundance of the species showed a sharp increase in the studied breeding-site – at the same time, the frequency of previously dominant species of the local larval assemblage (Ae. genicu-latus and Culex pipiens pipiens) declined. In the spring of 2018, the larval assemblage was already dominated by Ae. j. japonicus, and in the rest of the year, following a minor decline in September, the relative abundance of the species continued to increase. Based on our results, Ae. j. japonicus occupied rainwater collecting barrel which had been previously considered the main habitat for Cx. p. pipiens.