Multivariate curve resolution (MCR) was applied to (13)C cross-polarisation (CP) magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of non-depolymerised alginate powders obtained from brown seaweed plus a pure mannuronate sample isolated from Pseudomonas fluorescens for estimation of the mannuronic acid/guluronic acid ratio (M/G ratio). An excellent MCR model with a correlation coefficient of r(2)=0.99 was established between the estimated M/G ratios and the M/G ratios obtained from the traditional (1)H solution state NMR method. The new method allows for successful determination of the M/G ratio independent of the calcium content (at least up to 2.4%, which was the upper limit in this study) with a root mean square error of prediction of 0.05. It is thus concluded that (13)C CP-MAS NMR in combination with multivariate curve resolution is a reliable, convenient (no sample preparation is required) and relatively rapid method for M/G ratio determinations of alginates and it may serve as a good alternative to the chemical techniques traditionally used.