A guardrail assembly for a scaffold comprising standards, ledgers, and floor parts, the guardrail assembly comprising: - a guardrail extending along a longitudinal axis; - at least a first post and a second post each connected with the guardrail in a manner pivotable about a first pivoting point; - a mounting system for mounting the guardrail to a part of the scaffold, wherein the mounting system comprises a first and a second connector (12, 14) which are configured for engagement of a part of the scaffold (50, 52, 58), wherein the first post is connected with the first connector in a manner pivotable around a second pivoting point and wherein the second post is connected with the second connector in a manner pivotable around a further second pivoting point, wherein the guardrail, the at least first and second posts (34, 36) together form a parallelogram link system when the first and the second connector (12, 14) are connected with the scaffold; and - a lifting arm which is fixedly connected with the first post and which extends in line with the first post from the second pivoting point away from the first pivoting point for bringing the guardrail assembly from a collapsed position to an extended position and vice versa, characterized in that the guardrail assembly is configured to be in the collapsed position during the mounting of the guardrail assembly to the scaffold (50, 52, 58) by means of the first and the second connector (12, 14) engaging the part of the scaffold (50, 52, 58), wherein due to the first and second pivoting points (38, 40), the first and second posts (34, 36) and the guardrail can be collapsed parallel and against or close to each other, wherein by moving the lifting arm the first post will be erected whereby the guardrail is carried along and also the second post will erect. - a guardrail extending along a longitudinal axis; - at least a first post and a second post each connected with the guardrail in a manner pivotable about a first pivoting point; - a mounting system for mounting the guardrail to a part of the scaffold, wherein the mounting system comprises a first and a second connector (12, 14) which are configured for engagement of a part of the scaffold (50, 52, 58), wherein the first post is connected with the first connector in a manner pivotable around a second pivoting point and wherein the second post is connected with the second connector in a manner pivotable around a further second pivoting point, wherein the guardrail, the at least first and second posts (34, 36) together form a parallelogram link system when the first and the second connector (12, 14) are connected with the scaffold; and - a lifting arm which is fixedly connected with the first post and which extends in line with the first post from the second pivoting point away from the first pivoting point for bringing the guardrail assembly from a collapsed position to an extended position and vice versa, characterized in that the guardrail assembly is configured to be in the collapsed position during the mounting of the guardrail assembly to the scaffold (50, 52, 58) by means of the first and the second connector (12, 14) engaging the part of the scaffold (50, 52, 58), wherein due to the first and second pivoting points (38, 40), the first and second posts (34, 36) and the guardrail can be collapsed parallel and against or close to each other, wherein by moving the lifting arm the first post will be erected whereby the guardrail is carried along and also the second post will erect. characterized in that the guardrail assembly is configured to be in the collapsed position during the mounting of the guardrail assembly to the scaffold (50, 52, 58) by means of the first and the second connector (12, 14) engaging the part of the scaffold (50, 52, 58), wherein due to the first and second pivoting points (38, 40), the first and second posts (34, 36) and the guardrail can be collapsed parallel and against or close to each other, wherein by moving the lifting arm the first post will be erected whereby the guardrail is carried along and also the second post will erect.