In this study, nCaO(2) was synthesized successfully and applied in the Fe(II)-based catalytic environments in investigating trichloroethylene (TCE) removal performance. nCaO(2) with the particle sizes in the range of 50-200 nm was prepared, and it performed better for TCE removal when compared to the conventional CaO2. Further experimental results showed that 70.4% of TCE could be removed in 180 min at the nCaO(2)/Fe(II)/TCE molar ratio of 1/2/1, while this data was elevated to 86.1% in the presence of citric acid (CA) at the nCaO(2)/Fe(II)/CA/TCE molar ratio of 1/2/2/1 in the same test period. Probe compound tests, specifically designed for free radicals confirmation, demonstrated the presence of HO center dot and O-2(-center dot). Moreover, scavenging tests indicated that HO center dot was the major radical responsible for TCE degradation but O-2(-center dot) promoted the removal of TCE in both nCaO(2)/Fe(II) and nCaO(2)/Fe(II)-CA system. In addition, the effects of initial solution pH and anions (Cl-, HCO3-) were also evaluated. The performance of TCE degradation in actual groundwater demonstrated that both nCaO(2)/Fe(II) and nCaO(2)/Fe(II)-CA systems can be applicable for TCE removal in ISCO practice and the nCaO(2)/Fe(II)-CA system is much promising technique. These fundamental data strongly confirmed the feasibility and potential of nCaO(2) based technique in the remediation of TCE contaminated groundwater.