In terms of thermal behavior and char characteristics, co-pyrolysis of sewage sludge (SS) and rice straw (RS) to produce char samples has been evaluated in this study. Thermogravimetric analysis of the co-pyrolysis process indicated that the introduction of RS into co-pyrolysis with SS promoted the progress of co-pyrolysis by reducing the reaction activation energy, which also presented the synergistic effects during the co-pyrolysis process as a result of the migration of alkali metals. The char characteristics were analyzed by proximate analysis, elemental analysis, N-2 adsorption-desorption, X-ray diffraction patterns, scanning electron microscopy, and heavy metal behavior. The results showed that char samples from co-pyroysis of SS and RS with the high ash content and low heating value were not suitable for fuel. However, these char samples can be used for soil amendments as a result of the advantages of the increased C content, pH, and electrical conductivity values, the developed hierarchical porous structure, and the immobilization of heavy metals in char samples.