Simpler, cheaper, and fast methods to characterize material properties are important in industrial plants. One of these properties is molecular weight which is measured generally by size exclusion chromatography, an expensive method and also limited for polyolefins which have few solvents. Melt flow index (MFI) measurement is simple, cheap, and rapid that could be a considerable method to estimate (M) over barw of polymers. In this work, mathematical correlation between MI* (a new defined MFI), first melt dropping of blend (t(1)), weight fraction (w(i)) and (M) over barw in binary polyethylene blends, PE/PE wax, has been investigated by using a new device. Results show that relationships MI and t(1) with w(i) of the blended materials follow a modified Arrhenius equation (Wong equation) and also new non-Arrhenius equations for prediction of MI of blends have been investigated. We proposed a modified molecular weight (Mm) for Bremner and Rudin's equation (Bremner et al., J Appl Polymn Sci 1990, 41, 1617), which is used in 1/MI* and t(1) correlations with molecular weight of polymer. (C) 2008 Wiley Periodicals, Inc.