Organic phase change materials like polyethylene glycol (PEG) are unlikely to directly utilized in latent heat storage due to their low conductivity in nature. In this work, we proposed and experimentally studied a new synthesized silicon carbonitride (SiCN) to enhance the thermal energy storage and release rates. Firstly, SiCN were successfully made via high-temperature pyrolysis of a polysilazane precursor. Secondly, the composite phase change materials (CPCMs) composinig polyethylene glycol 6000 (PEG6000) and additive of SiCN with different mass fraction of SiCN (0, 0.5, 1, 2, and 5 wt%) were prepared by dispersing the as-prepared SiCN powder in liquid PEG6000. The results indicated that no chemical reaction existed between the PEG6000 and SiCN. The PEG6000 with 5 wt% SiCN was chosen as suitable CPCM, which melt at 62.3 degrees C with the latent heat of 147.1 J/g and solidified at 42.8 degrees C with solidification enthalpy of 139.5 J/g. Compared to pure PEG, no large latent heat of the composite lost even adding 5 wt% SiCN. The thermal cycle test implied that the CPCM with 5 wt% SiCN loading showed excellent thermal reliability and chemical stability after 100 thermal cycles. Furthermore, the thermal energy storage and release rates of the CPCMs (5 wt% SiCN loading) were enhanced by 64.5% and 59.4% compared to pure PEG6000. It was envisioned that the prepared SiCN/PEG composites have promising potential as PCMs in solar based heating, hot water and electronic applications.