In order to study the effect of time, number and tools of second tillage on one of the most harmful weeds in the rice (Juncus Sp.) fields of northern Iran. An experiment was conducted with a factorial statistical design in the form of complete randomized block design with three factors, eight treatments and three replications at Tonekabon area in the north of Iran. The three factors included; time of second tillage (20 days and 10 days before transplanting), number of second tillage (one time and two times), tools of second tillage (Rast kawl related tiller and equipped with iron wheels and rotivator). Results of variance analysis showed that times of second tillage had significant effects on dry matter of Juncus Sp. in the 30 days after transplanting. The variance analysis of data showed that tools of second tillage had significant effect on the percentage of rate Juncus Sp. in the 30 days after transplanting. According to the results of variance analysis, number of second tillage had effect on the percentage of dry matter Juncus Sp. before harvesting. So interaction of time and number of second tillage had effect on the percentage of dry matter Juncus Sp. before harvesting. Key words: Rice (Oryza sativa L.), time, number, tools, second tillage (Puddling), Juncus Sp. weed population.