Plastic waste from film packaging is one of the major threats to environmental sustainability. The problem can be reduced by using a biodegradable raw material such as starch to replace the non-biodegradable petroleum-based plastic. However, starch is highly hydrophilic and brittle, which needs to be modified to improve these drawbacks. In this research, a mixture of tapioca starch (S) and glycerol (G) was crosslinked with citric acid (CA) at different ratios (0, 0.4, 0.6, 0.8, 1.0 wt% of dry basis). Effects of CA contents on the degree of crosslinking, thermal stability, and tensile properties were investigated. The sample that contained 0.6 wt% CA showed the highest degree of crosslinking (i.e. 56 %), good thermal stability, high modulus (10 MPa) and tensile strength (0.16 MPa), and low elongation at break (161 %) when compared with other samples. Samples that have higher CA contents (i.e. 0.8 wt% and 1.0 wt%) experienced the acid hydrolysis on the crosslinking site, reducing the degree of crosslinking, thermal stabilities, and tensile properties.