There are technically no limits on the number of Event properties you can send to Mixpanel. However, the maximum number of properties you will be able to access in the Mixpanel UI drop-downs is 1500. Additionally there is a limit of 255 properties per event so while you can have different events containing different properties, each event is limited to 255 properties. These limits include Mixpanel default properties and Mixpanel special/reserved Properties. It is important to note that if you find yourself above 1500 total event properties and/or 255 properties per event, it is likely you will want revisit the naming of your properties as discussed in this article.
Keep in mind the number of Properties sent per Event does tie into the amount of data being used by the device sending data to Mixpanel. While this may not matter on a browser or on your server, it will impact the data consumption by your app on users’ mobile devices. Because of this, we recommend ensuring the Properties you send will never be uncapped and will always have a maximum length to avoid excess data consumption.
Mixpanel People Profiles can contain up to 255 properties each -- attempts to add more than 255 properties will fail. Additionally, only the 255 most common People Properties will be accessible in the Mixpanel UI drop-downs. As with Event Properties, these limits also include Mixpanel default People Properties.
While Event data (including Event Properties) are immutable, People Properties can be removed using the $unset engage operation if you find yourself close to the 255 per profile limit.