Urban heat island effect can be defined as a phenomenon of aggregating heat in urban sites caused by change of land cover and human activities, which is one of the most obvious characteristics of urban climate. Since increasing population enters into urban and super cities form consequently, urban heat island effect becomes more and more important. The increase of environmental temperature will certainly affect the physiology and even morphology of ornamental plants. Therefore, the experiments were carried out in two ornamental plants (Buxus megistophylla Lévl and Syzygium aromaticum), which respectively grew in urban heat island and urban cool island covered with abundant vegetation. During the growing season the environmental factors of urban heat island and urban cool island were observed, including , daytime temperature, nighttime temperature, soil temperature, soil volume water content, vapor pressure deficit and photosynthetically active radiation. The morphology characteristics of foliage of the two plants in urban heat island and urban cool island were investigated. Basing on the observation of biomass of whole foliage we further separated the foliage into three sections (lamina, mid-rib and petiole) to observe the allocation of biomass on different sections. Leaf nitrogen content of two plants in both urban heat island and urban cool island were also obtained in our study. Experimental results indicated that in urban heat island environmental temperature and were much higher than that in urban cool island obviously, whereas other environmental factors showed no significant difference. In urban heat island biomass of Buxus megistophylla Lévl and Syzygium aromaticum were 1.6 fold and 1.4 fold respectively compared to that in urban cool island. In addition to energy balance, overall foliage biomass investment between lamina and petiole was optimized. In urban heat island plants tended to allocate more biomass to lamina, but less to petiole. Furthermore, the allocation of dry mass per unit area also gave a significant difference, which could be described that plants in urban heat island tended to increase the allocation of dry mass per unit area on lamina, but decrease the allocation of dry mass per unit area on petiole. Plants in urban heat island exhibited larger foliage biomass as well as larger leaf area. However, further researches suggested that in contrast to urban cool island, in urban heat island foliage of plants exhibited lower specific leaf area. Many research works indicated that N_mass and N_area showed a highly positive relative relationship with the specific leaf area. Then in our research N_mass and N_area of plants in urban heat island both decreased along with the reduction of specific leaf area. N_area of Buxus megistophylla Lévl in urban heat island and urban cool island exhibited a significant difference (P<0.05). N_area of Buxus megistophylla Lévl in urban heat island was 0.73mg/g. Then N_area of Buxus megistophylla Lévl in urban cool island was 1.193mg/g. N_area of Buxus megistophylla Lévl and Syzygium aromaticum in urban heat island were both lower than that in urban cool island (P<0.05). Therefore, urban heat island effect obviously affected the morphology characteristics of plants, but the details of influence mechanism were unknown and further studies and discussions were still needed.