Muscle spasticity is a common motor disorder following upper motor neuron syndrome. A reliable and valid clinical tool is essential to document the effect of therapeutic interventions aimed to improve function by reducing spasticity. The Modified Ashworth Scale (MAS) is the most widely used and accepted clinical scale of spasticity. The MAS has been recently modified. The aim of this investigation was to determine the interrater and intrarater reliability of clinical test of knee extensor post-stroke spasticity graded on a Modified Modified Ashworth Scale (MMAS). Two raters scored the muscle spasticity of 15 patients with ischaemic stroke. For the inter- and intrarater reliability, two raters agreed on 80.1% and 86.6%, respectively. The Kappa values were good (kappa=0.72, SE=0.14, p<0.001) between raters and very good (kappa=0.82, SE=0.12, p<0.001) within one rater. The values of Kendall tau-b correlation were acceptable for clinical use with 0.87 (SE=0.06, p<0.001) between raters and 0.92 (SE=0.05, p<0.001) within one rater. The MMAS demonstrated reliable measurements for a single rater and between raters for measuring knee extensor post-stroke spasticity. The results encourage further study on the reliability and the validity of the scale.