The outcome of cryogenic treatment (CTT) on the mechanical behaviour of Al alloy LM 25, LM25+5% fly ash and LM25+10%fly ash composites was investigated. Cryogenic treatments were performed with threedifferent soaking periods (0 hr (Untreated), 12hr, 24hr) ata constant cryogenic temperature of -196°C. After the CTT, the mechanical behaviour of the materials was measured. It is obvious that LM25+10% fly ash composites exhibitbetter mechanical properties than the LM25 and LM25+10% fly ash composites.As cryogenic soaking period increases mechanical properties of the MMCs tend to increase too. The effect of fly ash mass percentage and cryogenic soaking period on the mechanical behaviour of materials was studied by using Taguchi and Analysis of Variance (ANOVA).