Abstract: This invention provides an online polymer monitoring apparatus for rapid determination of molecular weight and/or size, and/or other properties of importance to the polymer quality. The apparatus uses fast sample extraction, preparation and delivery techniques to convert complex polymer sample solution into the diluted polymer analyte solution. This analyte solution is then passed through the flow-through detectors for measurement of the polymer molecular weight, the polymer concentration and/or the identification and concentrations of the selected species of importance to the polymer quality. The continuous stream of the above measurement data, thus, allows accurate determination the status of the polymer for many polymer containing process streams, such as an ongoing polymerization reaction mixture, polymer resin fluid, melt or solid polymer flow.