This invention relates to a lens module and a LED illumination device using the same. The lens module includes a plurality of lens units and a plate. Each of the lens units includes a lens body, a first engaging structure and a second engaging structure. The lens body has a light incident surface at a top thereof and a light exit surface at a bottom thereof. The first and second engaging structures are arranged at peripheral edges of the lens body. On the other hand, the plate defines a plurality of seats for accommodating the lens units. Each of the seats includes an aperture from top to bottom of the plate to receive the respective lens body of the lens unit, a supporting structure arranged at peripheral edge of the aperture of the seat to engage with the respective first engaging structure of the lens in order to prevent the lens unit from falling off the seat, and a suppressing structure arranged at peripheral edge of the aperture of the seat to engage with the second engaging structure of the lens in order to prevent the lens unit from upward withdrawal of the seat.