To develop a highly sensitive seawater salinity sensor, a long period fiber grating (LPFG) was successfully fabricated using CO₂ laser technology to function in close proximity to the dispersion turning point (DTP). An LPFG operating near DTP was fabricated in an 80 μm single mode fiber using CO₂ laser micromachining technology. This successful endeavor demonstrates the feasibility of developing LPFG with shorter grating period using CO₂ laser micromaching technology. LPFGs with varying periods were fabricated by adjusting the preparation period of CO₂ laser to ensure that the cladding mode LP_1,9 was operating near DTP, resulting in higher refractive index sensitivity of LPFG. The average sensitivity of 0.279 nm/‰ can be achieved in the seawater with salinity ranging from 5.001‰ to 39.996‰, especially with the dual peaks resonance LPFG at a period of 115.4 μm, thanks to the dual peaks resonance effect. The dual peaks resonance LPFG seawater salinity sensor exhibits high sensitivity and a large attenuation loss, suggesting potential application in seawater salinity monitoring.