The Ocean Bottom Seismoemter (OBS) is a key instrument for geophysical study of sea sub-bottom layers. At present, more relaible autonomous equipment capable of staying underwater for long periods of time and therefore handling large data storage are needed. This paper presents a new Ocean Bottom Seismometer designed to be used in long period seismic surveys. Power consumption and noise level of the acquisition system are the key points to optimize the autonomy and the data quality. To achieve our goals, a new low power datalogger with high resolution and Signal–to-Noise Ratio (SNR) based on Compactflash memory card is designed to enable continous data acquisition. The equipment has been evaluated in the lab and is going to be used in real environmental conditions in second semester of 2011.