Stress-relaxation tests on Guadua angustifolia rings were conducted to determine the behavior under sustained transverse loading. A generalized Maxwell's model with three parameters showed good accuracy in fitting the experimental data. However, a significant dispersion of model parameters was observed. Thus, the Scott-Blair fractional derivative model with two parameters was formulated to fit the experimental data. Model fittings showed excellent approximations to experimental data (R2 = 0.996) with fewer parameters than a traditional model. Fractional models appear to be a good alternative to theoretically analyze the viscoelasticity of bamboo.