Forest thinning is a sylvicultural practice that aims to provide better growth space for increasing tree growth and stand quality. Forest thinning is a form of forest disturbance that has an impact on the forest environment, including flying insects. This study aimed to assess the impact of thinning of mixed forest stands on the diversity of flying insects. Eight circular plots of 0.1 ha were laid out systematically on thinning plots of 15.3 ha. Parameters observed in the plot included environment factors (stand composition, temperature, humidity, and canopy cover), abundance, species composition, and biodiversity index of flying insects (diversity index, species richness index, evenness index, and similarity index). The sweep net was used to collect the flying insects. Mann-Whitney test was used to compare the index of biodiversity of flying insects before and after forest thinning. Forest thinning caused a decrease in abundance, species composition, diversity index, richness index, and evenness index of flying insects. Forest thinning led to a decrease in the abundance of herbivorous flying insects and an increase in the abundance of predatory flying insects. Flying insect species found before thinning was not identical to those after thinning.Keywords: diversity index, flying insect, forest ecosystem, forest tending