A new analytical approach was proposed to monitor the reaction between epoxidized soybean oil and diethylene glycol in the presence of ZnCl2 as an epoxide ring opening catalyst for microwave assisted synthesis of polyol. Infrared spectra of the products were used as the input data, being processed by multivariate curve resolution – alternating least squares (MCR-ALS) for quantitative monitoring. The data obtained in different MW powers were analyzed by MCR factor analysis coupled with ALS optimization procedure. Standard deviation of residuals for experimental data and the variance explained at the optimum condition (r2) were 0.135 and 97.24% respectively.