In this application note, we study how accurately the DelsaMax CORE instrument can determine the molecular weight of monoclonal antibodies and common proteins. Accurate determination of the molecular weight of proteins and antibodies is typically very inaccurate and time-consuming; gel electrophoresis, the most popular method, requires calibration standards, is semi-qualitative, lacks sensitivity, and has numerous sources of error. By using the simultaneous Dynamic Light Scattering (DLS)/Static Light Scattering (SLS) system of the DelsaMax CORE, molecular weight measurements can be performed in just a few seconds at a wide range of concentrations and temperatures. The results demonstrate the extremely high accuracy and speed of the DelsaMax CORE for molecular weight determinations; while proteins and antibodies act as an example system, the molecular weight can be found for any biological molecule, polymer, or particle ranging from 300 Da up to 106 Da in molecular weight. The ability to obtain the molecular weight of molecular systems will be very valuable for molecular biologists looking at proteinprotein interactions and antibody-antigen interactions.