Biopolymers are a class of macromolecules produced by living organisms. These macromolecules are responsible for the biological functions of molecular motions, homeostasis, and catalysis. To improve biopolymers in the direction of higher performance and better functionality, understanding of their physicochemical behavior and their response to external stimuli are of great importance. In this study, the characteristics of several functional biopolymers such as hydroxyethylcellulose (HEC), its hydrophobically modified analogue (HM-HEC), dextran, hyaluronan (HA), and mucin have been investigated with the aid of rheology, rheo-small angle light scattering (SALS), dynamic light scattering (DLS), and small angle neutron scattering (SANS). To determine molecular weight and polydispersity index, asymmetric flow field-flow fractionation (AFFFF) was used. The characteristics of these functional biopolymers were studied under various external stimuli such as temperature, pH, cosolute, and chemical crosslinking.