Fast pyrolysis is one of the most promising ways for municipal sewage sludge (MSS) treatment and can generate bio-char as an important and beneficial product. The structure of bio-char determines its further utilization. Co-pyrolysis of MSS and wooden waste (WW) was carried out at 800 degrees C for bio-char preparation with different wet MSS/ WW mixing ratios. Both physical and chemical structural characteristics of the bio-chars were analyzed to reveal the evolution of bio-char structure during the co-pyrolysis. Results showed that the inherent moisture of MSS had gasification effect on the structure of bio-char generated from both MSS itself and WW With the increase of WW content, the BET surface area of bio-chars increased from 68.49 cm(2) g(-1) to 119.52 cm(2) g(-1) due to the high surface area of WW-char (150.59 cm(2) g(-1)). But the average pore sizes of all mixed samples were smaller than 10 nm, which indicated that the MSS-char particles would block the WW-char particles. According to the Raman spectra and XRD results, the inherent moisture was beneficial for the formation of functional groups (mainly carbonyl group) on the bio-char surface. However, the excess moisture led to the additional carbonaceous component consumption and decreased the Raman intensity.