Starting from Saturday, the 1 a.m.-6 a.m. curfew will be effective until July 26, according to statement by Deputy Minister for Civil Protection and Crisis Management Nikos Hardalias.
Moreover, around-the-clock music will not be allowed in clubs and bars on the island, reports Xinhua news agency.
Mykonos, along with Santorini, Crete, Paros and Ios, have witnessed a significant increase in Covid-19 cases in the last few days.
Between July 7-14, the daily infection rate jumped from 77 to 318 on Mykonos, according to Hardalias.
The increase is attributed to crowded parties in combination with the spreading of the highly contagious Delta variant across the country.
Gatherings of more than 20 persons for events in private, non-business places are still forbidden nationwide, said the press statement.
Violators face fines of up to 200,000 euros ($236,000).
Greece has imposed two nationwide lockdowns since the start of the pandemic.
The second one was being gradually relaxed from spring for the reopening of tourism and other sectors of the economy.
This month, the daily number of new infections across the country exceeded 3,000 for the first time in four months.