A bracelet assembly comprising: a base having two distal ends (21, 22), one of the two distal ends (21, 22) of the base having at least one reception portion and at least one notch which is located next to the at least one reception portion, the other one of the two distal ends (21, 22) of the base having at least one hole, a module part replaceably connected to the base and having two ends (31, 32), one of the two ends of the module part having at least one extension portion which extends through and is engaged with the at least one reception portion, the at least one extension portion having at least one first engaging member which is engaged with the at least one notch, the other one of the two ends having at least one second engaging member which is engaged with the at least one hole, the at least one first engaging member and the at least one second engaging member respectively facing two opposite directions, the bracelet assembly being characterized in that: a first protrusion is located between the at least one reception portion and the at least one notch, the at least one extension portion has a recessed area with which the first protrusion is engaged so that the at least one first engaging member is engaged with the at least one notch, and a second protrusion is located at a distal edge of the at least one reception portion, a recess is defined in a backside of the recessed area and the second protrusion is engaged with the recess, when the at least one extension portion is engaged with the at least one reception portion, the at least one second engaging member is engaged with the hole to connect the module part to the base. a base having two distal ends (21, 22), one of the two distal ends (21, 22) of the base having at least one reception portion and at least one notch which is located next to the at least one reception portion, the other one of the two distal ends (21, 22) of the base having at least one hole, a module part replaceably connected to the base and having two ends (31, 32), one of the two ends of the module part having at least one extension portion which extends through and is engaged with the at least one reception portion, the at least one extension portion having at least one first engaging member which is engaged with the at least one notch, the other one of the two ends having at least one second engaging member which is engaged with the at least one hole, the at least one first engaging member and the at least one second engaging member respectively facing two opposite directions, the bracelet assembly being characterized in that: a first protrusion is located between the at least one reception portion and the at least one notch, the at least one extension portion has a recessed area with which the first protrusion is engaged so that the at least one first engaging member is engaged with the at least one notch, and a second protrusion is located at a distal edge of the at least one reception portion, a recess is defined in a backside of the recessed area and the second protrusion is engaged with the recess, when the at least one extension portion is engaged with the at least one reception portion, the at least one second engaging member is engaged with the hole to connect the module part to the base. a first protrusion is located between the at least one reception portion and the at least one notch, the at least one extension portion has a recessed area with which the first protrusion is engaged so that the at least one first engaging member is engaged with the at least one notch, and a second protrusion is located at a distal edge of the at least one reception portion, a recess is defined in a backside of the recessed area and the second protrusion is engaged with the recess, when the at least one extension portion is engaged with the at least one reception portion, the at least one second engaging member is engaged with the hole to connect the module part to the base.