This study investigated the thermo-chemical degradation and fast pyrolysis of watermelon seed shells (WSS), pumpkin seed shells (PSS), and sunflower seed shells (SSS). The raw materials and pyrolysis products were analyzed. The results showed that the carbon content (52.96%), hydrogen content (7.38%) and higher heating value (HHV) (23.88 MJ/kg) of PSS were highest, and the bio-oil from the PSS pyrolysis had high amounts of phenolic compounds. For SSS, the content of holocellulose (83.47 wt.%) was the highest, but the lignin content (13.62 wt.%) was lower than the other samples. The gas yield from the SSS pyrolysis was the largest and the bio-oil content of acids (acetic acid 36.53%) and ketones (1-hydroxy-2-propanone 9.90%) were higher. For WSS, the yield of the biochar was 39.14 wt.%. Additionally, the raw materials’ structures were similar. The thermal decomposition process of all seed shells had three stages, i.e. dehydration, active pyrolysis, and passive pyrolysis. In all three kinds of bio-oil, the components were mainly guaiacol-type and phenol-type. The guaiacol-type in the bio-oils from PSS (43.78%) and WSS (32.33%) were higher than in the bio-oil from SSS.