Technical Abstract: Ultraviolet-B (UV-B) radiation reaching the Earth's surface has increased by 6-14% since 1980s and climate models project that UV-B will continue to rise in the near future. Many studies have evaluated the effects of increased UV-B radiation on plant growth and development, but its effect on plant biota is less known. To understand the increased UV-B radiation effects on reniform nematode (Rotylenchus reniformis Linford and Oliveira) populations, cotton (Gossypium hirsutum L.) plants were exposed to three levels of UV-B radiation [0 (control), 6 and 12 kJ m-2 d-1] in a glasshouse from emergence. At each UV-B treatment, four populations [0 (N0), 2500 (N2500), 5000 (N5000) and 7500 (N7500)] of reniform nematodes were incorporated into the sterilized rooting medium. Plant growth, development, photosynthetic parameters, pigments, phenolics and the number of eggs and nematode numbers in the rooting medium were recorded at the end of the experiment, 40 DAS. Even though, UV-B radiation did not significantly affect growth and development, it did significantly increase leaf and root phenolic concentrations. UV-B treatments significantly decreased both the egg and nematode numbers in all the nematode population treatments. Significant negative correlation was found between root phenolic concentrations and egg (r2 = 0.88) and nematode (r2 = 0.86) numbers. Similarly, leaf phenolics also showed significant negative trend with egg (r2 = 0.53) and nematode numbers (r2 = 0.47). Therefore, current and projected UV-B radiation levels may have an important regulatory influence on nematode populations.