OBJECTIVE： To study the effects of Cornus officinalis polysaccharide on learning and memory ability of vascular dementia （VD） model rats and its mechanism. METHODS： 30 rats were randomly divided into sham operation （normal saline） group， model （normal saline） group and C. officinalis polysaccharide （0.28 g/kg） group. Except sham operation group， VD model was induced in other groups and given relevant medicine intragastrically once a day. After 4 weeks， the frequency of leaping over original platform position， water maze mean escape latencies， platform retention time and average swimming distance were detected， and the mRNA and protein expression of brain-derived neurotrophic factor （BDNF） and apoptosis related gene Bcl-2 in hippocampal tissue of rats were determined. RESULTS： Compared with sham operation group， learning and memory ability of rats in model group weakened， manifesting as the frequency of leaping over original platform position decreased， water maze mean escape latencies prolonged， platform retention time shortened， average swimming distance extended （P＜0.05）； mRNA and protein expression of BDNF and Bcl-2 in hippocampus decreased significantly （P＜0.05）. Compared with model group， learning and memory ability of rats in C. officinalis polysaccharide group increased， manifesting as the frequency of leaping over original platform position increased， water maze mean escape latencies shortened， platform retention time prolonged， average swimming distance shortened （P＜0.05）； mRNA and protein expression of BDNF and Bcl-2 in hippocampus was enhanced significantly （P＜0.05）. CONCLUSIONS： C. officinalis polysaccharide can improve the learning and memory ability of VD rats， and its mechanism may be associated with the expression up-regulation of BDNF and Bcl-2 in hippocampus.