The cost and endurance anxiety about proton exchange membrane fuel cells (PEMFCs) has prompted the rapid development of platinum-based (Pt-based) oxygen reduction electrocatalysts towards smaller particle sizes, higher durability and alloying. However, well-balanced these advanced trends by a simple approach is difficult in practice, because the existing solutions are problematic in removing the protective organic coating or oxide shell that preventing the high-temperature agglomeration of Pt-based nanocrystals, or broadening the size range of Pt-based nanocrystals which caused by the heterogeneous distribution of heteroatom anchor points on supports. With a self-developed strategy that based on the atomic layer deposition (ALD), we have addressed these problems in two aspects. One is directly loading size and distribution controllable Pt nanocrystals on diverse supports, and another is indirectly depositing easily removed ultra-thin metal oxide coating with dual functions on prefabricated ultrasmall Pt nanocrystals to restrain their sintering effect during high temperature ordering. By controlling the temperature and pulse time of ALD, we successfully synthesized ultrasmall (< 2 nm) Pt nanocrystals on surface inactive TiC nanoparticles and nanowires. These two new electrocatalysts exhibited comparable oxygen reduction activity and durability on par with commercial Pt/C with lower Pt loading. And using this strategy, about 1 nm ZnO coating on Pt nanocrystals was performed to construct uniform PtZn intermetallic nanocrystals with the ultrasmall size of 2.50 ± 0.65 nm and excellent stability for oxygen reduction reaction. The mass activity of PtZn intermetallic nanocrystals reaches to 0.60 A mg_Pt^-1 at 0.9 V (6 times than commercial Pt/C) and only 13 mV decrease of half-wave potential after 30000 cycles of accelerated durability testing rivaling the most recently reported PtZn catalysts. Ultrasmall sizes and excellent features of our Pt and Pt-based intermetallic nanocrystals are all attributed to the accurate control of ALD and could be a promising method applying to other Pt-based intermetallic nanocrystals.