Low levels of ultraviolet-B (UV-B: 280–320 nm) radiation below the canopy in densely planted rice (Oryza sativa L.) fields have a negative impact on tiller initiation and development. Moreover, there is a varietal difference in the response to UV-B radiation in rice. Plants received no natural UV-B radiation due to the UV absorption characteristics of greenhouse glass, hence UV-B was artificially supplied by supplemental UV-B lighting. Rice plants were exposed to UV-B radiation of 0 (control), 4 (sub-ambient), or 8 (ambient) kJ m^-2d^-1. Results indicated no significant difference for plant height, tiller number per plant, chlorophyll content and leaf temperature between cultivars at 0 and 4 kJ m^-2d^-1. However, a significant difference was observed for the varieties at ambient UV-B radiation compared to the control for tiller number, plant height, and chlorophyll content. Our results show that UV-B radiation plays an important role in tiller initiation and development. Partially supported by the Texas Rice Belt Warehouse and Texas Rice Research Foundation.