Centella asiatica L. Urban (CA) is a valuable medicinal herb that contains various bioactive secondary metabolites. In the present study, the harvested CA was divided into whole plant and leaf parts, and were heated-air-dried or freeze-dried. The dried CA was extracted under various extraction conditions to obtain 16 extracts, and their antioxidant activities were examined. Twelve types of secondary metabolites (five polyphenolic acids, four triterpenoids, and three flavonoids) were quantified in each extract. Finally, the intercorrelations between secondary metabolites and antioxidant activities were analyzed through statistical analyses, such as Pearson correlation coefficient, scatter plotting, and principal component analysis. The antioxidant capacities of CA might be primarily influenced by major triterpenoids such as madecassoside and asiaticoside, which showed high content in the ethanol extracts of freeze-dried leaf parts. The present study provides a valuable groundwork for the development of optimal extraction processes for C. asiatica L. as an antioxidant material.