| Election Name: | 1900 Waihemo by-election |
| Country: | New Zealand |
| Flag Year: | 1900 |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | 1899 New Zealand general election |
| Previous Year: | 1899 general |
| Next Election: | 1902 New Zealand general election |
| Next Year: | 1902 general |
| Turnout: | 2,842 |
| Candidate1: | Thomas Mackenzie |
| Party1: | New Zealand Liberal Party |
| Popular Vote1: | 1,834 |
| Candidate2: | William Guffie |
| Party2: | Independent politician |
| Popular Vote2: | 1,008 |
| Member | |
| Before Election: | John McKenzie |
| After Election: | Thomas Mackenzie |
| Before Party: | New Zealand Liberal Party |
| After Party: | New Zealand Liberal Party |
The Waihemo by-election was a by-election in the New Zealand electorate of Waihemo, a rural seat in Otago, in the South Island.
The by-election was held on 18 July 1900, and was precipitated by the resignation of sitting MP, John McKenzie. The seat was won by fellow Liberal Thomas Mackenzie. Mackenzie was an advocate of the Otago province and campaigned to stop the region's declining situation compared to the rest of New Zealand. His sole opponent was William Guffie, a local councilor from Mount Ida.
The following table gives the election results: