In this research, we have investigated the influence of weak magnetic field (less than 0.55 T) at room temperature (300 K), on dynamical characteristics of semiconductor lasers (LD). The magnetic field has applied parallel and perpendicular on the axis of the active layer (region) of the LD chip. The LD used in this study is (Sanyo DL3149-056. ALGan P. Index Guided Multiple Quantum will active laser and had threshold current of 11.15 mA and slope efficiency of 189.4 mW/A). We observed that the optical power, threshold current, slope efficiency, and barrier potential were all had affected by the magnetic field (B). This study useful in several areas, including the indication of the existence of a magnetic field, the detection of magnetic fields especially in narrow region, which are difficult to detect by traditional techniques and can manufacture a micro-sensor to measure the weak magnetic fields. The LD uses in optical communication systems, visual information reading systems and magnetic field detection as an essential source of information transmission.