Tea polyphenols possess antioxidant properties and have been shown to have a protective effect against several degenerative diseases. The study aimed to determine the amounts of polyphenols and antioxidant properties for teas grown in Sri Lanka, over a period of 10 months. Water extracts of freeze-dried fresh (unfermented) and fully-fermented tea leaves were made for a structured set of samples (fermented and unfermented teas from six plantations; teas representing two harvesting seasons from four plantations) collected from the main tea growing regions in Sri Lanka. Total phenolic content (TPC), the ferric reducing antioxidant power (FRAP) and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity were determined for each sample. The results highlight significant (P < 0.05) variations in antioxidant activity across the six plantations. FRAP and DPPH for both fermented and unfermented teas from the four highland plantations showed a significant (P < 0.05) interaction between season and plantation. A similar interaction between season and plantation was observed for total phenolics in unfermented teas from the four highland plantations. The variability of the total phenolics for fermented teas, however, was independent of seasonal variations. A significant correlation (r = 0.5, P < 0.05) was observed between FRAP and total phenolics.