Dendrobium spp. are precious medicinal plants, used in China for thousands of years as health foods and nutrients. Polysaccharides are the main effective ingredients in Dendrobium plants. In this study, the chemical characteristics and the effects of crude polysaccharides (CPs) from five species of Dendrobium on macrophage function were investigated and compared in vitro for the first time. Chemical characteristic studies showed that CPs from different species of Dendrobium were diverse, displaying widely varied Mw distributions and molar ratios of monosaccharides. Their effects on macrophage functions, such as promoting phagocytosis, release of NO and cytokines IL-1α, IL-6, IL-10 and TNF-α, were also different. Moreover, CPs from D. officinale, especially collected from Yunnan Province, exerted the strongest immunomodulatory activities and could be explored as a novel potential functional food. The diverse chemical characteristics of CPs from different species of Dendrobium might contribute to their varied effects on macrophage functions, which should be further investigated.