In　this　paper,　a　novel　bi-directional　piezoelectric　energy　harvester　which　can　harvest　vibration　energy　bi-directionally　is　introduced　and　investigated　theoretically　and　experimentally.　The　proposed　harvester　is　composed　of　two　sub-systems:　a　main　beam　to　generate　electricity　and　a　spring-mass　oscillator　to　trigger　the　vibration　of　the　main　beam　from　an　additional　direction　by　using　magnets　to　couple　the　two　sub-systems.　The　theoretical　model　is　built　on　the　basis　of　the　Euler-Bernoulli　beam　theory　and　the　magnetic　charge　model.　A　prototype　is　fabricated　to　test　the　performance　of　the　harvester　experimentally.　Linear　upward　and　downward　frequency　sweeps　are　used　to　obtain　the　frequency　responses.　The　experimental　results　show　good　agreement　with　the　theoretical　model　under　frequency　sweeps.　A　comparison　with　a　beam-beam　bi-directional　piezoelectric　energy　harvester　is　also　performed　experimentally.　Although　both　bi-directional　piezoelectric　energy　harvesters　exhibit　the　capability　of　harvesting　vibration　energy　in　two　orthogonal　directions,　the　beam-spring　energy　harvester　shows　a　more　consistent　performance　in　both　directions　as　regards　the　bandwidth　and　amplitude　of　the　frequency　responses.