Introduction. Two field experiments were conducted to investigate the effects ofpotassium (K) on plant growth, fruit yield and quality of pineapple cultivated on tropical peat soil.Materials and methods. Six levels of K: 0, 266, 532, 798, 1064 and 1330 kg $\cdot$ ha-1 K2Owere applied at each of two pineapple plantations located at two different sites. The experiments wereconducted with the Gandul cv. in a randomized complete block design with three replications. Results anddiscussion. The application of K had not any significant effect on plant height and leaf number ofpineapple at both sites. Potassium significantly influenced the fruit diameter at site 1, and fruit lengthand fruit weight at site 2. The application of 266 kg $\cdot$ ha-1 K2O resulted in the highest fruitweight and, at site 2, further increase of K declined it. Potassium had no significant effect on fruitsugar and acidity. However, at site 2, acid content tended to increase with increased K applications.Conclusion. Potassium applications at high rates tended to depress most of the growth and yieldattributes of cv. Gandul pineapple cultivated on peat soil in Malaysia.