Fixatives may be classified into three types based on their chemical composition, type of structures fixed, and number of structures fixed. 

Based on chemical composition, fixatives may be classified as:

1. Physical agents – Heat and microwaves 
2. Oxidizing agents – Osmium tetroxide
3. Aldehydes – Formaldehyde, glutaraldehyde, acrolein
4. Coagulants – Acetic acid, ethyl alcohol, methyl alcohol, 
5. Miscellaneous – Mercuric acid, picric acid

Based on types of structures fixed, fixatives may be classified as: 

1. Cytologic fixatives – Clarke’s fluid, Flemming’s fluid, glacial acetic acid
2. Histochemical fixatives – Formaldehyde, glutaraldehyde, vapor fixatives
3. Microanatomical fixatives – Helly’s fluid, Bouin’s fluid, Heidenhain’s fluid, 

Based on number of structures fixed, fixatives may be classified as: 

1. Simple fixatives – Formaldehyde, picric acid, osmium tetroxide
2. Compound fixatives – Zenker’s fluid, Bouin’s fluid, formol saline