The volatile metabolites of green microalgae, Chlorella vulgaris, grown in outdoor condition were isolated by steam distillation and fractionated on a silica gel column (12´500mm) using different organic solvent mixtures. The volatile metabolites and obtained fractions were analyzed to identify their compositions using Gas liquid chromatography (GLC) and Gas Chromatography-Mass Spectrometry (GC/MS). Also, the influence of fractions at different concentration levels on µ-amylase activity  and coleoptile growth as well as germination of barley grains was evaluated. The obtained results showed that the volatile metabolites were a mixture of about 105 compounds of which 30 compounds were identified representing 86.38% of the total volatile components. These components were consisting of hydrocarbons, acids, alcohols, esters, aldhydes and ketones, which represented 32.86%, 23.93%, 15.62%, 8.02%, 3.24% and 2.71% of the total volatile components respectively. Hexadecene, octadec 9,12-dienoic, hexadecanol,  methyl octadecanote, hexadecanal and hexadecanone were the major components detected in their  fractions, respectively. The total volatile metabolites had a strong inhibitory action on the a-amylase activity and growth of coleoptile as well as germination of barley grains. On the other hand, the acid fraction had the highest inhibition effect compared with other fractions. In contrast, hydrocarbon fraction showed no effect in this respect.