Abstract: This study investigated the allelopathic effects of eucalyptol and limonene, two main terpenoids from cyanobacteria VOCs, on other algae by focusing on cell growth, absorption spectra of photosynthetic pigments and photosynthetic abilities using Chlamydomonas reinhardtii. Eucalyptol at 1.6 and 4 mmol/L as well as limonene at 0.4 and 0.8 mmol/L remarkably inhibited C. reinhardtii cell growth by 16.7%, 50.6%, 29.1% and 44.4%, respectively. Moreover, limonene at 1.6 and 4 mmol/L killed the cells. In addition, an obvious reduction was found in the absorption peaks at 413, 433, 457 and 663 nm. The components of photosynthetic pigments were degraded markedly, and xanthophyll even disappeared by 0.8 mmol/L limonene treatment. When C. reinhardtii cells were treated by eucalyptol and limonene, the fluorescence intensity from O to P was lower compared to the control, and it was declined with the increased compound concentration. In chlorophyll fluorescence transient parameters, φP_o, Ψ_o, φE_o, RC/CS_M, ABS/CS_M, TR_o/CS_M, ET_o/CS_Mand PI_ABS were declined remarkably, while DI_o/CS_M was raised remarkably, indicating that eucalyptol and limonene can inhibit the quantum production and electron transport in PSⅡ, and promote the absorbed solar energy to dissipate as heat. Therefore, eucalyptol and limonene might play allelopathic effects in cyanobacteria VOCs via inducing degradation of photosynthetic pigments and reducing photosynthetic abilities in other algae.