[Objective] To study the lipid metabolism mechanism regulated by Ubiquitin-conjugating Enzyme (E2) CrUBC23 in Chlamydomonas reinhardtii.[Methods] The mRNA levels of ubiquitin-conjugating enzyme CrUBC23 were analyzed by qRT-PCR under low nitrogen and low phosphorus conditions in C. reinhardtii. Fragments for RNAi interference and over-expression of CrUBC23 gene were cloned, and then the RNA interference vector and over-expression vector were constructed and transformed into C. reinhardtii. The biomass and lipid content of the transgenic strain was detected. The fusion expression vector CrUBC23-GFP was constructed also, and the subcellular localization of onion epidermal cells was carried out by using Agrobacterium tumefaciens.[Results] The level of RNA in C. reinhardtii were increased significantly under low nitrogen and low phosphorus conditions, with an increase of 4.98-5.80 times and 1.85-5.20 times as much as that in normal culture, respectively. RNA interference results showed that the neutral lipid content and total lipid content of transgenic algae decreased by 5.5% and 3.16%-17.6%. While, over-expression showed that the neutral lipid content increased by 8.8% and the total lipid content increased by 4.51%-14.03%.[Conclusion] CrUBC23 is a positive regulator in lipid metabolism, and may locate in the nucleus.