First of all, it depends on the grantor’s eligibility requirements on Principal Investigators (PIs).

Meanwhile, the University has set out the eligibility requirement on PIs of external research grants. According to Clause 5.1 of CUHK’s Policy on Research:

Academic staff at Assistant Professor rank or Research Assistant Professor rank or above may serve as Principal Investigators of externally supported research awards. Other staff members, with the approval of the immediate supervisor and the Chairperson of the Research Committee may serve as Principal Investigators under special circumstances, provided that a named full-time academic staff member at Associate Professor rank or Research Associate Professor rank or above assumes responsibility for ensuring that the administration of the award conforms with the sponsor's requirements.

Therefore, if the grantor concerned accepts a Postdoctoral Fellow being the PI, a Postdoctoral Fellow can be PI of external research grants after obtaining special approval from the Chairperson of the Research Committee.

For procedures for obtaining special approval, please contact Grants Team, ORKTS for information.