The use of nanoparticles is increasing worldwide. In particular, titanium dioxide nanoparticles (TiO2-NPs) have received considerable attention due to their extensive use. Temperature plays an important role as a modulator of biological processes. The aim of this study was to investigate the toxic effects of TiO2-NP on the decomposition of leaf litter and on the activity (respiration rate and enzyme activity) and diversity of microbial communities associated with decomposition of Ficus sycomorus leaves at two temperatures. During the experiment, the effect of four different concentrations (0, 1, 10, 100 mg/L) of TiO2-NP on leaves decomposition rate was measured at two different temperatures (25-26°C and 33-35 °C) in three incubation periods (2, 4, 6 weeks). The effects on percentage mass loss, respiration rate and bacterial and fungal count were measured in the three periods. The effects on enzyme activity, biomass of filamentous algae and bacterial diversity were measured only after six weeks of incubation. Both TiO2-NP concentration and temperature affected leaf decomposition rate in weeks two and four, By week six, there was no significant effect because leaves already decomposed. Also, there was a significant direct effect of time on percentage mass loss. The respiration rate of microbes associated with Ficus sycomorus leaves was significantly affected by time of exposure, NP concentrations and temperature. The overall bacterial and fungal counts associated with leaf were very low. No significant effect of NP concentrations and exposure periods was observed on bacterial count but there was a significant effect of temperature on bacterial count as the bacterial count in high temperature was higher than in low temperature. However, there was no significant effect of NP concentration or temperature on the fungal count and biomass of algae. The data from MiSeq Illimina sequencing of the bacterial communities found 5895.8 operational taxonomic units (OTUS) that corresponded to 7 classes, 20 genus, and 28 species. Bacterial species number and species richness estimates increased at high temperature and there are higher class and genus variations in high temperature treatments than in low temperature. Bacteria belonging to class Alphaproteobacteria were found to be the dominant class at both high and low temperatures. Our findings indicate that bacterial activity and diversity could be used as environmental indicators to assess the contamination of aquatic ecosystems with NPS and that the change of environmental conditions particularly rises in water temperature might increase the negative impacts of the nanoparticles.