The abandoned limestone quarry from Bycioc is located near the village, along the left side of Nistru river and represent the largest complex of mines on the territory of the Republic of Moldova. The mines have more than 30 entrances and stretch over the distance of 3.5 km. The size of entrances varies between 0.5 m and 4 m height and between 3 m and 5.5 m width. The quarries and have been excavated mechanically with special machines, the underground galleries have the height of 2.5 – 6 m, the width of 3 – 7 m and the maximum depth of 5 km. The cracks left after the machine saws are elongated, more or less symmetrically disposed with the width of 3-5 cm and 7-15 cm depth, where bat individuals are located. The temperature and humidity near the entrances fluctuate depending on the season, while at 50-m and deeper they are relatively constant: temperature is of +780C and humidity is of 65%.  The studies were performed the second decade of March 2019, at the end of hibernation period, when the bats start to be active and to hunt insects during night. In general, the hibernation process begins in October – November, depending on the weather and food availability, and ends in March. The weather was very warm for this period: outside the entrances the temperature was of +22.40C and the humidity was of 35%, it was sunny with southwest wind direction an low intensity. The bats were studied directly by visual observations, all observed individuals were identified. Hibernation places were recorded, the distance from the entrance, crowding of individuals (single or in groups), the number of individuals of each species were noted. Animals were not removed from the shelters, to not disturb the hibernation process.In total 69 individuals from 4 species were registered: Myotis daubentoni (water bat), M. dasycneme (pond bat), Eptesicus serotinus (serotine bat) and Rhinolophus hipposideros (lesser horseshoe bat). The dominant species was M. daubentoni with 83%, followed by E. serotinus with 13%, M. dasycneme with 3% and Rh. hipposideros with only 1%. The closest to the entrance (at 15 m) was an individual of serotine bat, while the lesser horseshoe bat was observed in the deeper places of the mine (about 130 m). From 4 registered species 3 are listed in the Red Book of the Republic of Moldova (2015): Rh. hipposideros [EN], Myotis daubentoni [VU] and M. dasycneme [EN]. All the species are listed in Annex II of Bern Convention, in Appendix II of Bonn Convention on Migratory species, while in the list of Emerald Network two species are listed: Rh. hipposideros and M. dasycneme. Unfortunately, at the quarries entrances and several dozen meters inside there was a rubbish dump that was not present in previous years of study. Therefore, the number and diversity of the bats was much lower in comparison to the same period of 2014, when 150 individuals from 5 species have been registered (Nistreanu et al., 2015; 2016). Thus, the waste pollution has a strong negative influence on bat species and populations. During the last 60 years the abandoned limestone quarry from Bycioc is one of the most significant underground bat roosts in Moldova, where hundreds of individuals from 8 species hibernate (Averin, Lozan, 1965; Dorosenco, 1975; Andreev, Vasiliev, 1997, Nistreanu et al., 2015; 2016). The monitoring of bat communities at Bycioc site will continue. In order to protect bats in artificial underground roosts, it is necessary to raise the ecological consciousness of the local authorities and population, of tourists about the role of bats in nature and in human economy, about the consequences of pollution. The study was performed within the fundamental project 15.187.02.11F at the Institute of Zoology of the Republic of Moldova.