Blood-derived products, particularly platelet-rich plasma (PRP), have received increased attention in the past several years due to their great potential as a therapy for osteoarthritis and tendon injuries. Therefore, characterizing the mechanical properties of PRP becomes important to better understand its therapeutic efficacy. This paper aims to investigate the rheological properties of PRP in order to provide further insight into its mechanism of action. The PRP samples in our study may have higher erythrocyte count than the average PRP reported in the literature. Flow-sweep, small amplitude oscillatory shear (SAOS), large amplitude oscillatory shear (LAOS), and thixotropy tests have been performed at room and physiological temperatures to characterize the non-Newtonian properties of PRP samples. Flow-sweep tests reveal shear-thinning behavior, with higher apparent viscosity observed at a lower temperature. Rheological models such as Carreau, Casson, power-law, and Herschel-Bulkley have been fitted to flow-sweep data with the latter showing the closest agreement. Over the acceptable narrow range of frequency in SAOS tests, the loss modulus appears to be slightly larger than the storage modulus with both moduli decreasing at higher temperature. The nonlinear viscoelastic properties are furthermore quantified through the static and dynamic LAOS analyses. For a given strain and angular frequency, the former identifies strain-softening and shear-thinning, while the latter discloses a range of other transient behavior within an oscillation cycle. Lastly, peak-hold tests have revealed consistent thixotropy in PRP solutions.