Forestation in the increasingly urbanized area generates a huge demand for ornamental tree stocks, requiring new approach to promote the cultural efficiency of highly valued seedlings. Chitosan oligo-saccharide (COS) is one of biodegradable natural plant growth modifier derived from chitin and an abundant water insoluble biopolymer. In this study, Buddhist pine (Podocarpus macrophyllus) (PM) and Northeast yew (Taxus cuspidata) (TC) were cultured with or without COS addition from 1 July to 17 November 2016. Relative to the TC seedlings, the PM seedlings had greater growth of height and biomass which was found to be negatively correlated with the changes of nitrogen (N) and phosphorus (P) concentrations in shoot during the culture. Only those TC seedlings treated without COS addition had higher proportion of decline in the initial N concentration than that in the PM seedlings. Root P concentration declined less in Buddhist pine seedlings than that in Northeast yew seedlings treated with COS. By 17 of November 2016, both N and P seemed to have been diluted in the PM seedlings and exceed the demand in the TC seedlings. In conclusion, COS had the potential to be used for the culture of ornamental tree seedlings to promote nu-trient utilization for shoot biomass accumulation, but more specific effect on nutrient allocation and utiliza-tion need to be confirmed by more studies.