a lighting device and a back light module therewith are disclosed . the back light module includes a light - guiding structure and a lighting device . the light - guiding structure includes two light - guiding parts and a reflection sheet disposed therebetween . the lighting device is disposed close to the light - guiding structure and includes an insulation carrier and two light sources disposed on the insulation carrier . the insulation carrier includes a positioning groove structure where an edge of the reflection sheet is disposed such that the two light sources correspond to the two light - guiding parts respectively and light emitted by the two light sources is capable of entering the corresponding light - guiding parts . thereby , the invention uses the single - structure lighting device to simultaneously provide required light to the two light - guiding parts respectively , and uses the positioning structure formed on the lighting device to improve the assembly preciseness of the light - guiding structure with the lighting device .