A sample analyzer includes: a preparation unit configured to mix a sample with a reagent to prepare a measurement specimen; a measurement unit configured to irradiate the measurement specimen with light to acquire optical time series data; and a controller configured to divide the time series data acquired by the measurement unit into data segments, determine first regression lines respectively of the data segments, select the first regression line with the highest matching degree with the time series data, set as an analysis target region a region of the time series data matching with the selected first regression line among the time series data acquired by the measurement unit, determine a second regression line using the time series data included in the set analysis target region, and perform an analysis using the second regression line.