Biofuel industry is gradually growing as the market starts to shift the demand from non-renewable energy sources to renewable energy sources The aim of this study is to produce bioethanol from biomass feedstock which is Leucaena leucocephala. It is a potential lignocellulosic energy source as it contains high composition of carbohydrates which can be broken down into fermentable sugar through pretreatment and enzymatic hydrolysis prior to the fermentation into bioethanol. Screening for both upstream processing were conducted by OFAT experiments to optimize several parameters tested such as pretreatment temperatures and NaOH concentrations. Fermentation process was conducted in Simultaneous Saccharification and Fermentation (SSF) conditions aided by Kluyveromyces marxianus UniMAP 1-1 as the fermenting microbes. This yeast is capable in converting sugar to ethanol at high temperature. The optimization of pretreatment and enzymatic hydrolysis by using OFAT gave the optimum value for both process prior to fermentation. The ethanol obtained from this SSF Fermentation is 3.15 g/L of bioethanol from 25.0 g/L of total sugars in hydrolysate. This report provides further information in the interest of producing bioethanol from Leucaena leucocephala seeds using Kluyveromyces marxianus UniMAP 1-1.