The Whanganui Regional Museum in Whanganui, New Zealand, has an extensive collection of natural and human-history objects. The emphasis is on items from the Manawatū-Whanganui region, but the collection also includes objects of national and international significance, such as Pacific tapa, ceramics from Asia and Cyprus, and moa bones from nearby Makirikiri Swamp.

Local naturalist and jeweller Samuel Henry Drew was instrumental in establishing the museum; his private collection was sold to the town, and he was honorary curator when the then-Wanganui Public Museum opened on 24 March 1895. The original building was on the site of the present Savage Club Hall.

A new building on Watt Street near Queen's Park was constructed in 1928. Designed by architect Robert Talboys, the building had two stories and a basement. The museum was renamed the 'Alexander Museum', after Henry Alexander as the new build was funded with monies from his estate.

The move to the new museum brought about a change in exhibit. Previously stored collections were displayed, such as the McLachlan collection of coins. A newspaper article at the time reported that the collection of British coins was the largest in the Southern Hemisphere and included coins from the Roman period right up to the 1920s. It had been collected over 150 years by three generations of the McLachlan family. Other previously displayed exhibits, like the three metre tall moa skeleton, were moved into storage.

In 1932, two escaped prisoners hid in the museum, posing as visitors. Their unkempt appearance and lack of interest in the displays, however, aroused suspicion in the director, J. Burnet, who then identified one of the men from a newspaper photograph.

A bequest from the Davis Trust funded the rear extension in 1968, which included a Māori Court, Davis Lecture Theatre, classroom, and a 2,000m² multi-storied car park. In 1997, the carpark was converted into storage facilities for the museum and Wanganui District Council's archive department.

In September 2016 the museum was closed to the public for earthquake strengthening, reconstruction and refurbishment, with exhibitions continuing at the old Post Office building at 62 Ridgway Street. The $2.6 million project was initially scheduled to take 18 months, but the reopening date was subsequently pushed forward to October 2018 and January 2019; it reopened in March 2019.

The museum has an internationally notable collection of moa bones, as many were found in the local area and not traded or dispersed as happened in other localities. The moa collection was documented and analysed in 1989 by palaeontologist Trevor Worthy, who was able to group the bones statistically into age and species classes.