The homogeneous, intensity modulated salinity sensor using the photonic crystal ring resonator (PCRR) is proposed and designed for monitoring the salinity of the seawater from 0% to 100% (0 g/L to 100 g/L) at 25 ℃. The concentration of the salinity in the seawater changes the refractive index of the seawater. The change in the refractive index of the seawater brings the change in the output signal intensity of the sensor as the seawater flows inside the sensor. By detecting the output power and mapping the salinity level, the salinity can be evaluated. The proposed sensor is composed of periodic Si rods embedded in an air host with a circular PCRR placed between the inline quasi waveguides. Approximately, 2.69% of output power reduction is observed for every 5% (5 g/L) increase in the salinity as the seawater has a unique refractive index for each salt level. With this underlying principle, the performance of the sensor is analyzed for different temperatures.