This study was carried out to evaluate growth response of a mixed culture of Spirulina platensis TISTR 8217 and Chroococcus minor TISTR 8574 to a mixture of naphthalene (NAP) and anthracene (ANT). Batch experiments were performed for 7 d in BG-11 medium amended with NAP and ANT (0–75 mg/L) at 28˚C under 12-h photoperiod of 3,000 lx. The cyanobacteria could grow with a mixture of 5 mg/L NAP and 5 mg/L ANT, showing a minor decrease in their biomass, chlorophyll-a and total protein content as compared to the controls. Meanwhile, cyanobacterial growth considerably decreased as NAP and ANT became more concentrated. Initial medium pH was also observed to affect cyanobacterial growth. The cyanobacteria grew well at pH 7.4 but appeared to show a reduction in growth as concentrations of NAP and ANT mixtures were above 5 mg/L, suggesting that NAP and ANT had high-dose inhibition (above 5 mg/L) on cyanobacterial growth. Moreover, NAP and ANT at concentrations above 25 mg/L caused high oxidative stress levels to the cyanobacteria.