The singularity of the collection of the Museu de Alberto Sampaio, mainly composed of pieces of religious art, derives from its unity and homogeneity, from being unusually well documented and furthermore for including a representative sample of local production.  About 70% of the total number of pieces originates from a single institution – the Insigne e Real Colegiada de Nossa Senhora da Oliveira – and the liturgical implements coming from Santa Marinha da Costa and from S. Torcato, or from the church of S. Miguel do Castelo, ended up being integrated in the treasure of the Collegiate Church; the temple of the Collegiate Church was the headquarters of the Irmandade de S. Nicolau, whose silverware was deposited in the Museum in 1994, forming a secondary nucleus within the collection.

The treasure of Our Lady of the Olive Tree, with pieces that go from the 12^th to the 19^th centuries, was created thanks to successive donations by kings, priors, canons, or simple faithful, or else its manufacture was commissioned by the church to answer devotional needs. It is regrettable that many of the works of art that formerly comprised it have disappeared but this treasure is sufficient to testify to the liturgical splendour of the most important ecclesiastical institution in Guimarães, to document various cultural realities and artistic sensibilities, and to evoke stories of faith, power and personal affirmation.

In this collection, one must highlight the magnificent silver gilt triptych, a present offered by Dom João I to Saint Mary of the Olive Tree to thank Her for the victory attained at the Battle of Aljubarrota in 1385.