Aims: To compare the in vitro fermentation properties of pectins and oligosaccharides derived from them in pure and mixed faecal cultures. Methods and Results: Specific growth rates of selected bacterial genera were calculated in pure culture. Bifidobacterium angulatum , B. infantis and B. adolescentis had higher growth rates on pectic oligosaccharides (POS I) derived from high methylated pectin (HMP) than on HMP and B. pseudolongum and B. adolescentis on pectic oligosaccharides (POS II) derived from low methylated pectin than on HMP. Controlled pH batch mixed faecal cultures were then carried out and a prebiotic index was calculated as a mean to compare the fermentation properties of the different substrates. In general, greater fermentation selectivity was obtained with lower degrees of methylation (PI24(-HMP) = -0.11, PI24(-LMP) = 0.033; PI24(-POS I) = 0.071 and PI24-POS II = 0.092). An effect of size on prebiotic potential was observed, with the oligosaccharides having more selective fermentation properties than the pectins they derived from. Conclusions: The degree of methylation plays an important role in the fermentation properties of pectins. Pectic-oligosaccharides are a better prebiotic candidate than the pectins, although their bifidogenic effect is low compared to oligofructose. Significance and Impact of the Study: The effect of size on prebiotic potential was demonstrated. Non-selectively fermented polysaccharides like pectin can have their bifidogenic properties improved by partial hydrolysis.