A self-adjusting, water pressure-responsive weight belt assembly for use in diving is disclosed. The assembly includes a tensioning portion comprising a housing and a reciprocating member reciprocatingly disposed within the housing. The housing comprises a cover and a hollow base to which one end of a flexible belt portion is attached. An end of the reciprocating member is situated external of the housing by being disposed in a position partially outside of the reciprocating member housing cover through a slot defined therein. The other end of the flexible belt portion is attached to one end of the reciprocating member. An air space of variable volume exists within the housing and is defined by the inner walls of the reciprocating member housing base and an end wall of the reciprocating member. The reciprocating member moves within the housing, thereby adjusting the fit of the assembly on the diver in response to changes in water pressure.