To test whether drought and ABA application alter the effects of enhanced UV‐B on the growth and biomass allocation ofPopulus yunnanensisDode, cuttings were grown in pots at two ABA levels, two watering regimes and two UV‐B levels for one growth season. Exposure to enhanced UV‐B radiation significantly decreased plant growth and photosynthesis under well‐watered conditions, but these effects were obscured by drought, which alone caused growth reduction. Drought may contribute to masking the effects of UV‐B radiation. The accumulation of UV‐B absorbing compounds and the increase of the ABA content induced by drought could reduce the effectiveness of UV‐B radiation. ABA application did not have large direct effects on biomass accumulation and allocation. Evidence for interactions between UV‐B and ABA was detected for only a few measured traits. Therefore, there was little evidence to support a pivotal role for ABA in regulating a centralized whole plant response to enhanced UV‐B. Yet, we recorded an ABA‐induced decrease in stomatal conductance (gs) and increase in UV‐B absorbing compounds and carbon isotope composition (δ13C) in response to enhanced UV‐B. The allometric analysis revealed that regression models between root and shoot biomass in response to enhanced UV‐B are different for plants under well‐watered and drought conditions. Enhanced UV‐B led to a significant displacement of the allometric regression line under well‐watered condition, while allometric trajectories for both UV‐B regimes did not differ significantly under drought condition.