Abstract: In this study, the authors proposed and experimentally demonstrated an encrypted Direct Detection-optical orthogonal frequency division multiplexing (DD-OOFDM) system based on Low Density Parity Check (LDPC) coding and logistic sequence. The long irregular LDPC code is used to enhance the correction capability of the system. The logistic sequence is adopted for the secure key which is sensitive to the initial condition. It can achieve a secure transmission at physical layer in the DD-OOFDM system for data encrypting. A 2.5 Gb sec^-1 16-QAM data with LDPC coding and logistic mapped is transmitted over 40 km SSMF successfully. The experimental results show that the LDPC coding cannot offer good performances of the BER without the correct logistic key.