Background: Soft Laser has been advantageous in medical applications and is widely used in clinical practice. It is applied because it doesn't cause the significant thermal effects or tissue hurt when irradiated. The blood response to low power laser radiation provides information about processes of laser radiation interaction with live creatures. Objective: The aim of the current work was to evaluate the laser-induced changes of in vitro erythrocyte sedimentation rate (ESR), mean corpuscular volume (MCV), and mean corpuscular hemoglobin concentration (MCHC) in patients with breast cancer by irradiating a human blood sample using a green laser and comparing its effects before and after irradiation with the same power density (100mW/cm²) and wavelength (532nm) of laser light. Materials and methods: Fresh blood samples of 30 cancer breast females were collected in EDTA tubes and divided into four equal quantities; one as a control sample and the other three for irradiation with laser at various exposure time. The blood parameters were measured by automatic hematology analyzer and ESR values were measured by using a Westergren method. Results: The MCV values were increased, the MCHC values were decreased and the ESR values were decreased significantly with increased exposure time. Conclusion: The change in blood parameters at various irradiated times with different doses using Soft Lasers with a532nm wavelength for breast cancer patients, are helpful to explain decrease in the ESR values induced by Soft Laser in phototherapy and give information about how the laser interaction with biological tissues.