Phytonutrients and pigments present in cyanobacteria act as antioxidants, which facilitate the formation of body's defense mechanism against free radical damage to cells. The aim of this investigation was to study the total phenolic content (
TPC
), total flavonoid content (
TFC
), antioxidant activity, phycobiliproteins (
PBP
s), and active compounds in four cyanobacterial species, that is,
Oscillatoria
sp.,
Lyngbya
sp.,
Microcystis
sp., and
Spirulina
sp. isolated from fresh water bodies of Sri Lanka. In this study,
Lyngbya
sp.
,
showed highest
TPC
(5.02 ± 0.20 mg/g),
TFC
(664.07 ± 19.76 mg/g), and total
PBP
s (127.01 mg/g) value. The ferric reducing antioxidant power (
FRAP
) was recorded highest in
Oscillatoria
sp. (39.63 ± 7.02), whereas the 2,2‐diphenyl‐1‐picrylhydrazyl (
DPPH
) radical scavenging activity was also reported the highest in
Oscillatoria
sp. (465.31 ± 25.76) followed by
Lyngbya
sp. (248.39 ± 11.97). In
FTIR
spectroscopy,
Lyngbya
sp. does not show any N‐H stretching band which is ultimately responsible for the inhibition of antioxidant activity. The study revealed that
Lyngbya
sp. and
Oscillatoria
sp. can be an excellent source for food, pharmaceutical, and other industrial uses.