Two kinds of alkyl substitution quinacridone derivative C6DHQA and C16DMQA X-type Langmuir-Blodgett (LB) films are prepared. The optical characteristics are studied by UV-visual spectrum, steady state and time resolved fluorescence. The experimental results show that the absorption spectrum of the C16DMQA has a whole red shift compared with C6DHQA′s. It shows that the energy level is lower with the added alkyl chain. The absorption spectrum of their LB films has a whole red shift compared with their solution. It shows that the two kinds molecule formed J-aggregation in LB films. The two kinds of material in chloroform solution and LB films both have strong flourescence emission. The absorption spectrum and the flourescence spetrum of the two kinds of material solution have mirror symmetry. But their LB films′s are asymmetrical. The third peak relative intensity of C6DHQA and C16DMQA LB films has a larger difference. The fluorescence lifetime at three fluorescenct emission peaks of C6DHQA solution is about 21 ns and C16DMQA′s is about 22 ns. It is obviously reduced as in LB films. And it is obviously diffrerent at the third peaks of C6DHQA compared with C16DMQA. All these differences are due to closer-arrangement of C16DMQA molecule on the substrate, the intermolecular interactions stronger and has a bigger influence on its energy level structure than C6DHQA molecule.