Recently, mode division multiplexing (MDM) has been introduced into optical transmission systems and networks for capacity enhancement. In this letter, we propose a bidirectional passive optical network (PON) architecture based on MDM. The bidirectional optical distribution network (ODN) of the MDM-PON consists of few-mode fiber, passive mode multiplexer/demultiplexer and few-mode circulators (FMCs), all of which are characterized by low modal-crosstalk. Signals in different modes are able to be transmitted and received independently for both downstream and upstream transmission. We experimentally demonstrate the bidirectional MDM-PON transmission over 10-km 2-mode optical fiber. 10-Gb/s on-off-keying (OOK) signals can be independently transmitted and directly detected without coherent receiver and multi-input-multiple-output (MIMO) processing. Moreover, nonlinear transmission impairments are experimentally investigated.