This chapel has seen a number of changes over the years. Originally this was the baptistery, where new Christians were baptised into the Church. Then in 1907 the font was moved out (although it was subsequently returned and is still there today) and the chapel redecorated to house a large and fine collection of relics and antiquities which had been bequeathed to the parish by Hartwell de la Garde Grissell. Over the years, the chapel suffered from neglect, and in 1971 the collection of antiquities was dispersed, and the relics burnt.

More recently, the chapel has begun to be restored. We were fortunate to obtain from the Carmelite convent at Chichester a collection of relics, as well as a wrought-iron screen to replace the one which had been scrapped. This was installed in late 1994.

A survivor from the Grissell collection is the picture of Our Lady of Oxford, which hangs over the altar. In recent years, devotion to Our Lady of Oxford, Mother of Mercy, has increased, and prayers for her intercession are said after the morning Mass on most Saturdays.

Also in this chapel is the statue of the patron saint of the church, St Aloysius Gonzaga.

The second chapel on the aisle is St Philip's chapel.