The formation of J-aggregates in the mutual mixing LB films of [6Me-DS](1-x)[DO](x), [DS](1-x) [DO](x) have been studied by optical absorbance, fluorescence and surface pressure-area isotherms. Here, 6Me-DS, DS and DO show three types of surface active merocyanine dyes. Both sharp J-band absorbance and fluorescence, being observed in the [6Me-DS] film, linearly shift to the longer wavelength for the replacement of [6Me-DS] by [DO]. On the other hand, in the [DS]-[DO] system, the shift of J-band peak is not monotonic and the peak intensity is once reduced by adding [DO], but enhanced at the 1:1 composition. At that composition a strong fluorescence is also detected, suggesting the well defined aggregates. In the pressure-area isotherms, characteristic reduction in the molecular occupying area is also observed in [DS](0.5)[DO](0.5). The reduction may be ascribed to enhancement of the molecular ordering.